[sql] Import reference version of SQLite 3.17..

third_party/sqlite/sqlite-src-3170000/src/fkey.c

+/*
+**
+** The author disclaims copyright to this source code.  In place of
+** a legal notice, here is a blessing:
+**
+**    May you do good and not evil.
+**    May you find forgiveness for yourself and forgive others.
+**    May you share freely, never taking more than you give.
+**
+*************************************************************************
+** This file contains code used by the compiler to add foreign key
+** support to compiled SQL statements.
+*/
+#include "sqliteInt.h"
+
+#ifndef SQLITE_OMIT_FOREIGN_KEY
+#ifndef SQLITE_OMIT_TRIGGER
+
+/*
+** Deferred and Immediate FKs
+** --------------------------
+**
+** Foreign keys in SQLite come in two flavours: deferred and immediate.
+** If an immediate foreign key constraint is violated,
+** SQLITE_CONSTRAINT_FOREIGNKEY is returned and the current
+** statement transaction rolled back. If a 
+** deferred foreign key constraint is violated, no action is taken 
+** immediately. However if the application attempts to commit the 
+** transaction before fixing the constraint violation, the attempt fails.
+**
+** Deferred constraints are implemented using a simple counter associated
+** with the database handle. The counter is set to zero each time a 
+** database transaction is opened. Each time a statement is executed 
+** that causes a foreign key violation, the counter is incremented. Each
+** time a statement is executed that removes an existing violation from
+** the database, the counter is decremented. When the transaction is
+** committed, the commit fails if the current value of the counter is
+** greater than zero. This scheme has two big drawbacks:
+**
+**   * When a commit fails due to a deferred foreign key constraint, 
+**     there is no way to tell which foreign constraint is not satisfied,
+**     or which row it is not satisfied for.
+**
+**   * If the database contains foreign key violations when the 
+**     transaction is opened, this may cause the mechanism to malfunction.
+**
+** Despite these problems, this approach is adopted as it seems simpler
+** than the alternatives.
+**
+** INSERT operations:
+**
+**   I.1) For each FK for which the table is the child table, search
+**        the parent table for a match. If none is found increment the
+**        constraint counter.
+**
+**   I.2) For each FK for which the table is the parent table, 
+**        search the child table for rows that correspond to the new
+**        row in the parent table. Decrement the counter for each row
+**        found (as the constraint is now satisfied).
+**
+** DELETE operations:
+**
+**   D.1) For each FK for which the table is the child table, 
+**        search the parent table for a row that corresponds to the 
+**        deleted row in the child table. If such a row is not found, 
+**        decrement the counter.
+**
+**   D.2) For each FK for which the table is the parent table, search 
+**        the child table for rows that correspond to the deleted row 
+**        in the parent table. For each found increment the counter.
+**
+** UPDATE operations:
+**
+**   An UPDATE command requires that all 4 steps above are taken, but only
+**   for FK constraints for which the affected columns are actually 
+**   modified (values must be compared at runtime).
+**
+** Note that I.1 and D.1 are very similar operations, as are I.2 and D.2.
+** This simplifies the implementation a bit.
+**
+** For the purposes of immediate FK constraints, the OR REPLACE conflict
+** resolution is considered to delete rows before the new row is inserted.
+** If a delete caused by OR REPLACE violates an FK constraint, an exception
+** is thrown, even if the FK constraint would be satisfied after the new 
+** row is inserted.
+**
+** Immediate constraints are usually handled similarly. The only difference 
+** is that the counter used is stored as part of each individual statement
+** object (struct Vdbe). If, after the statement has run, its immediate
+** constraint counter is greater than zero,
+** it returns SQLITE_CONSTRAINT_FOREIGNKEY
+** and the statement transaction is rolled back. An exception is an INSERT
+** statement that inserts a single row only (no triggers). In this case,
+** instead of using a counter, an exception is thrown immediately if the
+** INSERT violates a foreign key constraint. This is necessary as such
+** an INSERT does not open a statement transaction.
+**
+** TODO: How should dropping a table be handled? How should renaming a 
+** table be handled?
+**
+**
+** Query API Notes
+** ---------------
+**
+** Before coding an UPDATE or DELETE row operation, the code-generator
+** for those two operations needs to know whether or not the operation
+** requires any FK processing and, if so, which columns of the original
+** row are required by the FK processing VDBE code (i.e. if FKs were
+** implemented using triggers, which of the old.* columns would be 
+** accessed). No information is required by the code-generator before
+** coding an INSERT operation. The functions used by the UPDATE/DELETE
+** generation code to query for this information are:
+**
+**   sqlite3FkRequired() - Test to see if FK processing is required.
+**   sqlite3FkOldmask()  - Query for the set of required old.* columns.
+**
+**
+** Externally accessible module functions
+** --------------------------------------
+**
+**   sqlite3FkCheck()    - Check for foreign key violations.
+**   sqlite3FkActions()  - Code triggers for ON UPDATE/ON DELETE actions.
+**   sqlite3FkDelete()   - Delete an FKey structure.
+*/
+
+/*
+** VDBE Calling Convention
+** -----------------------
+**
+** Example:
+**
+**   For the following INSERT statement:
+**
+**     CREATE TABLE t1(a, b INTEGER PRIMARY KEY, c);
+**     INSERT INTO t1 VALUES(1, 2, 3.1);
+**
+**   Register (x):        2    (type integer)
+**   Register (x+1):      1    (type integer)
+**   Register (x+2):      NULL (type NULL)
+**   Register (x+3):      3.1  (type real)
+*/
+
+/*
+** A foreign key constraint requires that the key columns in the parent
+** table are collectively subject to a UNIQUE or PRIMARY KEY constraint.
+** Given that pParent is the parent table for foreign key constraint pFKey, 
+** search the schema for a unique index on the parent key columns. 
+**
+** If successful, zero is returned. If the parent key is an INTEGER PRIMARY 
+** KEY column, then output variable *ppIdx is set to NULL. Otherwise, *ppIdx 
+** is set to point to the unique index. 
+** 
+** If the parent key consists of a single column (the foreign key constraint
+** is not a composite foreign key), output variable *paiCol is set to NULL.
+** Otherwise, it is set to point to an allocated array of size N, where
+** N is the number of columns in the parent key. The first element of the
+** array is the index of the child table column that is mapped by the FK
+** constraint to the parent table column stored in the left-most column
+** of index *ppIdx. The second element of the array is the index of the
+** child table column that corresponds to the second left-most column of
+** *ppIdx, and so on.
+**
+** If the required index cannot be found, either because:
+**
+**   1) The named parent key columns do not exist, or
+**
+**   2) The named parent key columns do exist, but are not subject to a
+**      UNIQUE or PRIMARY KEY constraint, or
+**
+**   3) No parent key columns were provided explicitly as part of the
+**      foreign key definition, and the parent table does not have a
+**      PRIMARY KEY, or
+**
+**   4) No parent key columns were provided explicitly as part of the
+**      foreign key definition, and the PRIMARY KEY of the parent table 
+**      consists of a different number of columns to the child key in 
+**      the child table.
+**
+** then non-zero is returned, and a "foreign key mismatch" error loaded
+** into pParse. If an OOM error occurs, non-zero is returned and the
+** pParse->db->mallocFailed flag is set.
+*/
+int sqlite3FkLocateIndex(
+  Parse *pParse,                  /* Parse context to store any error in */
+  Table *pParent,                 /* Parent table of FK constraint pFKey */
+  FKey *pFKey,                    /* Foreign key to find index for */
+  Index **ppIdx,                  /* OUT: Unique index on parent table */
+  int **paiCol                    /* OUT: Map of index columns in pFKey */
+){
+  Index *pIdx = 0;                    /* Value to return via *ppIdx */
+  int *aiCol = 0;                     /* Value to return via *paiCol */
+  int nCol = pFKey->nCol;             /* Number of columns in parent key */
+  char *zKey = pFKey->aCol[0].zCol;   /* Name of left-most parent key column */
+
+  /* The caller is responsible for zeroing output parameters. */
+  assert( ppIdx && *ppIdx==0 );
+  assert( !paiCol || *paiCol==0 );
+  assert( pParse );
+
+  /* If this is a non-composite (single column) foreign key, check if it 
+  ** maps to the INTEGER PRIMARY KEY of table pParent. If so, leave *ppIdx 
+  ** and *paiCol set to zero and return early. 
+  **
+  ** Otherwise, for a composite foreign key (more than one column), allocate
+  ** space for the aiCol array (returned via output parameter *paiCol).
+  ** Non-composite foreign keys do not require the aiCol array.
+  */
+  if( nCol==1 ){
+    /* The FK maps to the IPK if any of the following are true:
+    **
+    **   1) There is an INTEGER PRIMARY KEY column and the FK is implicitly 
+    **      mapped to the primary key of table pParent, or
+    **   2) The FK is explicitly mapped to a column declared as INTEGER
+    **      PRIMARY KEY.
+    */
+    if( pParent->iPKey>=0 ){
+      if( !zKey ) return 0;
+      if( !sqlite3StrICmp(pParent->aCol[pParent->iPKey].zName, zKey) ) return 0;
+    }
+  }else if( paiCol ){
+    assert( nCol>1 );
+    aiCol = (int *)sqlite3DbMallocRawNN(pParse->db, nCol*sizeof(int));
+    if( !aiCol ) return 1;
+    *paiCol = aiCol;
+  }
+
+  for(pIdx=pParent->pIndex; pIdx; pIdx=pIdx->pNext){
+    if( pIdx->nKeyCol==nCol && IsUniqueIndex(pIdx) && pIdx->pPartIdxWhere==0 ){ 
+      /* pIdx is a UNIQUE index (or a PRIMARY KEY) and has the right number
+      ** of columns. If each indexed column corresponds to a foreign key
+      ** column of pFKey, then this index is a winner.  */
+
+      if( zKey==0 ){
+        /* If zKey is NULL, then this foreign key is implicitly mapped to 
+        ** the PRIMARY KEY of table pParent. The PRIMARY KEY index may be 
+        ** identified by the test.  */
+        if( IsPrimaryKeyIndex(pIdx) ){
+          if( aiCol ){
+            int i;
+            for(i=0; i<nCol; i++) aiCol[i] = pFKey->aCol[i].iFrom;
+          }
+          break;
+        }
+      }else{
+        /* If zKey is non-NULL, then this foreign key was declared to
+        ** map to an explicit list of columns in table pParent. Check if this
+        ** index matches those columns. Also, check that the index uses
+        ** the default collation sequences for each column. */
+        int i, j;
+        for(i=0; i<nCol; i++){
+          i16 iCol = pIdx->aiColumn[i];     /* Index of column in parent tbl */
+          const char *zDfltColl;            /* Def. collation for column */
+          char *zIdxCol;                    /* Name of indexed column */
+
+          if( iCol<0 ) break; /* No foreign keys against expression indexes */
+
+          /* If the index uses a collation sequence that is different from
+          ** the default collation sequence for the column, this index is
+          ** unusable. Bail out early in this case.  */
+          zDfltColl = pParent->aCol[iCol].zColl;
+          if( !zDfltColl ) zDfltColl = sqlite3StrBINARY;
+          if( sqlite3StrICmp(pIdx->azColl[i], zDfltColl) ) break;
+
+          zIdxCol = pParent->aCol[iCol].zName;
+          for(j=0; j<nCol; j++){
+            if( sqlite3StrICmp(pFKey->aCol[j].zCol, zIdxCol)==0 ){
+              if( aiCol ) aiCol[i] = pFKey->aCol[j].iFrom;
+              break;
+            }
+          }
+          if( j==nCol ) break;
+        }
+        if( i==nCol ) break;      /* pIdx is usable */
+      }
+    }
+  }
+
+  if( !pIdx ){
+    if( !pParse->disableTriggers ){
+      sqlite3ErrorMsg(pParse,
+           "foreign key mismatch - \"%w\" referencing \"%w\"",
+           pFKey->pFrom->zName, pFKey->zTo);
+    }
+    sqlite3DbFree(pParse->db, aiCol);
+    return 1;
+  }
+
+  *ppIdx = pIdx;
+  return 0;
+}
+
+/*
+** This function is called when a row is inserted into or deleted from the 
+** child table of foreign key constraint pFKey. If an SQL UPDATE is executed 
+** on the child table of pFKey, this function is invoked twice for each row
+** affected - once to "delete" the old row, and then again to "insert" the
+** new row.
+**
+** Each time it is called, this function generates VDBE code to locate the
+** row in the parent table that corresponds to the row being inserted into 
+** or deleted from the child table. If the parent row can be found, no 
+** special action is taken. Otherwise, if the parent row can *not* be
+** found in the parent table:
+**
+**   Operation | FK type   | Action taken
+**   --------------------------------------------------------------------------
+**   INSERT      immediate   Increment the "immediate constraint counter".
+**
+**   DELETE      immediate   Decrement the "immediate constraint counter".
+**
+**   INSERT      deferred    Increment the "deferred constraint counter".
+**
+**   DELETE      deferred    Decrement the "deferred constraint counter".
+**
+** These operations are identified in the comment at the top of this file 
+** (fkey.c) as "I.1" and "D.1".
+*/
+static void fkLookupParent(
+  Parse *pParse,        /* Parse context */
+  int iDb,              /* Index of database housing pTab */
+  Table *pTab,          /* Parent table of FK pFKey */
+  Index *pIdx,          /* Unique index on parent key columns in pTab */
+  FKey *pFKey,          /* Foreign key constraint */
+  int *aiCol,           /* Map from parent key columns to child table columns */
+  int regData,          /* Address of array containing child table row */
+  int nIncr,            /* Increment constraint counter by this */
+  int isIgnore          /* If true, pretend pTab contains all NULL values */
+){
+  int i;                                    /* Iterator variable */
+  Vdbe *v = sqlite3GetVdbe(pParse);         /* Vdbe to add code to */
+  int iCur = pParse->nTab - 1;              /* Cursor number to use */
+  int iOk = sqlite3VdbeMakeLabel(v);        /* jump here if parent key found */
+
+  /* If nIncr is less than zero, then check at runtime if there are any
+  ** outstanding constraints to resolve. If there are not, there is no need
+  ** to check if deleting this row resolves any outstanding violations.
+  **
+  ** Check if any of the key columns in the child table row are NULL. If 
+  ** any are, then the constraint is considered satisfied. No need to 
+  ** search for a matching row in the parent table.  */
+  if( nIncr<0 ){
+    sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, iOk);
+    VdbeCoverage(v);
+  }
+  for(i=0; i<pFKey->nCol; i++){
+    int iReg = aiCol[i] + regData + 1;
+    sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iOk); VdbeCoverage(v);
+  }
+
+  if( isIgnore==0 ){
+    if( pIdx==0 ){
+      /* If pIdx is NULL, then the parent key is the INTEGER PRIMARY KEY
+      ** column of the parent table (table pTab).  */
+      int iMustBeInt;               /* Address of MustBeInt instruction */
+      int regTemp = sqlite3GetTempReg(pParse);
+  
+      /* Invoke MustBeInt to coerce the child key value to an integer (i.e. 
+      ** apply the affinity of the parent key). If this fails, then there
+      ** is no matching parent key. Before using MustBeInt, make a copy of
+      ** the value. Otherwise, the value inserted into the child key column
+      ** will have INTEGER affinity applied to it, which may not be correct.  */
+      sqlite3VdbeAddOp2(v, OP_SCopy, aiCol[0]+1+regData, regTemp);
+      iMustBeInt = sqlite3VdbeAddOp2(v, OP_MustBeInt, regTemp, 0);
+      VdbeCoverage(v);
+  
+      /* If the parent table is the same as the child table, and we are about
+      ** to increment the constraint-counter (i.e. this is an INSERT operation),
+      ** then check if the row being inserted matches itself. If so, do not
+      ** increment the constraint-counter.  */
+      if( pTab==pFKey->pFrom && nIncr==1 ){
+        sqlite3VdbeAddOp3(v, OP_Eq, regData, iOk, regTemp); VdbeCoverage(v);
+        sqlite3VdbeChangeP5(v, SQLITE_NOTNULL);
+      }
+  
+      sqlite3OpenTable(pParse, iCur, iDb, pTab, OP_OpenRead);
+      sqlite3VdbeAddOp3(v, OP_NotExists, iCur, 0, regTemp); VdbeCoverage(v);
+      sqlite3VdbeGoto(v, iOk);
+      sqlite3VdbeJumpHere(v, sqlite3VdbeCurrentAddr(v)-2);
+      sqlite3VdbeJumpHere(v, iMustBeInt);
+      sqlite3ReleaseTempReg(pParse, regTemp);
+    }else{
+      int nCol = pFKey->nCol;
+      int regTemp = sqlite3GetTempRange(pParse, nCol);
+      int regRec = sqlite3GetTempReg(pParse);
+  
+      sqlite3VdbeAddOp3(v, OP_OpenRead, iCur, pIdx->tnum, iDb);
+      sqlite3VdbeSetP4KeyInfo(pParse, pIdx);
+      for(i=0; i<nCol; i++){
+        sqlite3VdbeAddOp2(v, OP_Copy, aiCol[i]+1+regData, regTemp+i);
+      }
+  
+      /* If the parent table is the same as the child table, and we are about
+      ** to increment the constraint-counter (i.e. this is an INSERT operation),
+      ** then check if the row being inserted matches itself. If so, do not
+      ** increment the constraint-counter. 
+      **
+      ** If any of the parent-key values are NULL, then the row cannot match 
+      ** itself. So set JUMPIFNULL to make sure we do the OP_Found if any
+      ** of the parent-key values are NULL (at this point it is known that
+      ** none of the child key values are).
+      */
+      if( pTab==pFKey->pFrom && nIncr==1 ){
+        int iJump = sqlite3VdbeCurrentAddr(v) + nCol + 1;
+        for(i=0; i<nCol; i++){
+          int iChild = aiCol[i]+1+regData;
+          int iParent = pIdx->aiColumn[i]+1+regData;
+          assert( pIdx->aiColumn[i]>=0 );
+          assert( aiCol[i]!=pTab->iPKey );
+          if( pIdx->aiColumn[i]==pTab->iPKey ){
+            /* The parent key is a composite key that includes the IPK column */
+            iParent = regData;
+          }
+          sqlite3VdbeAddOp3(v, OP_Ne, iChild, iJump, iParent); VdbeCoverage(v);
+          sqlite3VdbeChangeP5(v, SQLITE_JUMPIFNULL);
+        }
+        sqlite3VdbeGoto(v, iOk);
+      }
+  
+      sqlite3VdbeAddOp4(v, OP_MakeRecord, regTemp, nCol, regRec,
+                        sqlite3IndexAffinityStr(pParse->db,pIdx), nCol);
+      sqlite3VdbeAddOp4Int(v, OP_Found, iCur, iOk, regRec, 0); VdbeCoverage(v);
+  
+      sqlite3ReleaseTempReg(pParse, regRec);
+      sqlite3ReleaseTempRange(pParse, regTemp, nCol);
+    }
+  }
+
+  if( !pFKey->isDeferred && !(pParse->db->flags & SQLITE_DeferFKs)
+   && !pParse->pToplevel 
+   && !pParse->isMultiWrite 
+  ){
+    /* Special case: If this is an INSERT statement that will insert exactly
+    ** one row into the table, raise a constraint immediately instead of
+    ** incrementing a counter. This is necessary as the VM code is being
+    ** generated for will not open a statement transaction.  */
+    assert( nIncr==1 );
+    sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
+        OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
+  }else{
+    if( nIncr>0 && pFKey->isDeferred==0 ){
+      sqlite3MayAbort(pParse);
+    }
+    sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
+  }
+
+  sqlite3VdbeResolveLabel(v, iOk);
+  sqlite3VdbeAddOp1(v, OP_Close, iCur);
+}
+
+
+/*
+** Return an Expr object that refers to a memory register corresponding
+** to column iCol of table pTab.
+**
+** regBase is the first of an array of register that contains the data
+** for pTab.  regBase itself holds the rowid.  regBase+1 holds the first
+** column.  regBase+2 holds the second column, and so forth.
+*/
+static Expr *exprTableRegister(
+  Parse *pParse,     /* Parsing and code generating context */
+  Table *pTab,       /* The table whose content is at r[regBase]... */
+  int regBase,       /* Contents of table pTab */
+  i16 iCol           /* Which column of pTab is desired */
+){
+  Expr *pExpr;
+  Column *pCol;
+  const char *zColl;
+  sqlite3 *db = pParse->db;
+
+  pExpr = sqlite3Expr(db, TK_REGISTER, 0);
+  if( pExpr ){
+    if( iCol>=0 && iCol!=pTab->iPKey ){
+      pCol = &pTab->aCol[iCol];
+      pExpr->iTable = regBase + iCol + 1;
+      pExpr->affinity = pCol->affinity;
+      zColl = pCol->zColl;
+      if( zColl==0 ) zColl = db->pDfltColl->zName;
+      pExpr = sqlite3ExprAddCollateString(pParse, pExpr, zColl);
+    }else{
+      pExpr->iTable = regBase;
+      pExpr->affinity = SQLITE_AFF_INTEGER;
+    }
+  }
+  return pExpr;
+}
+
+/*
+** Return an Expr object that refers to column iCol of table pTab which
+** has cursor iCur.
+*/
+static Expr *exprTableColumn(
+  sqlite3 *db,      /* The database connection */
+  Table *pTab,      /* The table whose column is desired */
+  int iCursor,      /* The open cursor on the table */
+  i16 iCol          /* The column that is wanted */
+){
+  Expr *pExpr = sqlite3Expr(db, TK_COLUMN, 0);
+  if( pExpr ){
+    pExpr->pTab = pTab;
+    pExpr->iTable = iCursor;
+    pExpr->iColumn = iCol;
+  }
+  return pExpr;
+}
+
+/*
+** This function is called to generate code executed when a row is deleted
+** from the parent table of foreign key constraint pFKey and, if pFKey is 
+** deferred, when a row is inserted into the same table. When generating
+** code for an SQL UPDATE operation, this function may be called twice -
+** once to "delete" the old row and once to "insert" the new row.
+**
+** Parameter nIncr is passed -1 when inserting a row (as this may decrease
+** the number of FK violations in the db) or +1 when deleting one (as this
+** may increase the number of FK constraint problems).
+**
+** The code generated by this function scans through the rows in the child
+** table that correspond to the parent table row being deleted or inserted.
+** For each child row found, one of the following actions is taken:
+**
+**   Operation | FK type   | Action taken
+**   --------------------------------------------------------------------------
+**   DELETE      immediate   Increment the "immediate constraint counter".
+**                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
+**                           throw a "FOREIGN KEY constraint failed" exception.
+**
+**   INSERT      immediate   Decrement the "immediate constraint counter".
+**
+**   DELETE      deferred    Increment the "deferred constraint counter".
+**                           Or, if the ON (UPDATE|DELETE) action is RESTRICT,
+**                           throw a "FOREIGN KEY constraint failed" exception.
+**
+**   INSERT      deferred    Decrement the "deferred constraint counter".
+**
+** These operations are identified in the comment at the top of this file 
+** (fkey.c) as "I.2" and "D.2".
+*/
+static void fkScanChildren(
+  Parse *pParse,                  /* Parse context */
+  SrcList *pSrc,                  /* The child table to be scanned */
+  Table *pTab,                    /* The parent table */
+  Index *pIdx,                    /* Index on parent covering the foreign key */
+  FKey *pFKey,                    /* The foreign key linking pSrc to pTab */
+  int *aiCol,                     /* Map from pIdx cols to child table cols */
+  int regData,                    /* Parent row data starts here */
+  int nIncr                       /* Amount to increment deferred counter by */
+){
+  sqlite3 *db = pParse->db;       /* Database handle */
+  int i;                          /* Iterator variable */
+  Expr *pWhere = 0;               /* WHERE clause to scan with */
+  NameContext sNameContext;       /* Context used to resolve WHERE clause */
+  WhereInfo *pWInfo;              /* Context used by sqlite3WhereXXX() */
+  int iFkIfZero = 0;              /* Address of OP_FkIfZero */
+  Vdbe *v = sqlite3GetVdbe(pParse);
+
+  assert( pIdx==0 || pIdx->pTable==pTab );
+  assert( pIdx==0 || pIdx->nKeyCol==pFKey->nCol );
+  assert( pIdx!=0 || pFKey->nCol==1 );
+  assert( pIdx!=0 || HasRowid(pTab) );
+
+  if( nIncr<0 ){
+    iFkIfZero = sqlite3VdbeAddOp2(v, OP_FkIfZero, pFKey->isDeferred, 0);
+    VdbeCoverage(v);
+  }
+
+  /* Create an Expr object representing an SQL expression like:
+  **
+  **   <parent-key1> = <child-key1> AND <parent-key2> = <child-key2> ...
+  **
+  ** The collation sequence used for the comparison should be that of
+  ** the parent key columns. The affinity of the parent key column should
+  ** be applied to each child key value before the comparison takes place.
+  */
+  for(i=0; i<pFKey->nCol; i++){
+    Expr *pLeft;                  /* Value from parent table row */
+    Expr *pRight;                 /* Column ref to child table */
+    Expr *pEq;                    /* Expression (pLeft = pRight) */
+    i16 iCol;                     /* Index of column in child table */ 
+    const char *zCol;             /* Name of column in child table */
+
+    iCol = pIdx ? pIdx->aiColumn[i] : -1;
+    pLeft = exprTableRegister(pParse, pTab, regData, iCol);
+    iCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
+    assert( iCol>=0 );
+    zCol = pFKey->pFrom->aCol[iCol].zName;
+    pRight = sqlite3Expr(db, TK_ID, zCol);
+    pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
+    pWhere = sqlite3ExprAnd(db, pWhere, pEq);
+  }
+
+  /* If the child table is the same as the parent table, then add terms
+  ** to the WHERE clause that prevent this entry from being scanned.
+  ** The added WHERE clause terms are like this:
+  **
+  **     $current_rowid!=rowid
+  **     NOT( $current_a==a AND $current_b==b AND ... )
+  **
+  ** The first form is used for rowid tables.  The second form is used
+  ** for WITHOUT ROWID tables.  In the second form, the primary key is
+  ** (a,b,...)
+  */
+  if( pTab==pFKey->pFrom && nIncr>0 ){
+    Expr *pNe;                    /* Expression (pLeft != pRight) */
+    Expr *pLeft;                  /* Value from parent table row */
+    Expr *pRight;                 /* Column ref to child table */
+    if( HasRowid(pTab) ){
+      pLeft = exprTableRegister(pParse, pTab, regData, -1);
+      pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, -1);
+      pNe = sqlite3PExpr(pParse, TK_NE, pLeft, pRight);
+    }else{
+      Expr *pEq, *pAll = 0;
+      Index *pPk = sqlite3PrimaryKeyIndex(pTab);
+      assert( pIdx!=0 );
+      for(i=0; i<pPk->nKeyCol; i++){
+        i16 iCol = pIdx->aiColumn[i];
+        assert( iCol>=0 );
+        pLeft = exprTableRegister(pParse, pTab, regData, iCol);
+        pRight = exprTableColumn(db, pTab, pSrc->a[0].iCursor, iCol);
+        pEq = sqlite3PExpr(pParse, TK_EQ, pLeft, pRight);
+        pAll = sqlite3ExprAnd(db, pAll, pEq);
+      }
+      pNe = sqlite3PExpr(pParse, TK_NOT, pAll, 0);
+    }
+    pWhere = sqlite3ExprAnd(db, pWhere, pNe);
+  }
+
+  /* Resolve the references in the WHERE clause. */
+  memset(&sNameContext, 0, sizeof(NameContext));
+  sNameContext.pSrcList = pSrc;
+  sNameContext.pParse = pParse;
+  sqlite3ResolveExprNames(&sNameContext, pWhere);
+
+  /* Create VDBE to loop through the entries in pSrc that match the WHERE
+  ** clause. For each row found, increment either the deferred or immediate
+  ** foreign key constraint counter. */
+  pWInfo = sqlite3WhereBegin(pParse, pSrc, pWhere, 0, 0, 0, 0);
+  sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, nIncr);
+  if( pWInfo ){
+    sqlite3WhereEnd(pWInfo);
+  }
+
+  /* Clean up the WHERE clause constructed above. */
+  sqlite3ExprDelete(db, pWhere);
+  if( iFkIfZero ){
+    sqlite3VdbeJumpHere(v, iFkIfZero);
+  }
+}
+
+/*
+** This function returns a linked list of FKey objects (connected by
+** FKey.pNextTo) holding all children of table pTab.  For example,
+** given the following schema:
+**
+**   CREATE TABLE t1(a PRIMARY KEY);
+**   CREATE TABLE t2(b REFERENCES t1(a);
+**
+** Calling this function with table "t1" as an argument returns a pointer
+** to the FKey structure representing the foreign key constraint on table
+** "t2". Calling this function with "t2" as the argument would return a
+** NULL pointer (as there are no FK constraints for which t2 is the parent
+** table).
+*/
+FKey *sqlite3FkReferences(Table *pTab){
+  return (FKey *)sqlite3HashFind(&pTab->pSchema->fkeyHash, pTab->zName);
+}
+
+/*
+** The second argument is a Trigger structure allocated by the 
+** fkActionTrigger() routine. This function deletes the Trigger structure
+** and all of its sub-components.
+**
+** The Trigger structure or any of its sub-components may be allocated from
+** the lookaside buffer belonging to database handle dbMem.
+*/
+static void fkTriggerDelete(sqlite3 *dbMem, Trigger *p){
+  if( p ){
+    TriggerStep *pStep = p->step_list;
+    sqlite3ExprDelete(dbMem, pStep->pWhere);
+    sqlite3ExprListDelete(dbMem, pStep->pExprList);
+    sqlite3SelectDelete(dbMem, pStep->pSelect);
+    sqlite3ExprDelete(dbMem, p->pWhen);
+    sqlite3DbFree(dbMem, p);
+  }
+}
+
+/*
+** This function is called to generate code that runs when table pTab is
+** being dropped from the database. The SrcList passed as the second argument
+** to this function contains a single entry guaranteed to resolve to
+** table pTab.
+**
+** Normally, no code is required. However, if either
+**
+**   (a) The table is the parent table of a FK constraint, or
+**   (b) The table is the child table of a deferred FK constraint and it is
+**       determined at runtime that there are outstanding deferred FK 
+**       constraint violations in the database,
+**
+** then the equivalent of "DELETE FROM <tbl>" is executed before dropping
+** the table from the database. Triggers are disabled while running this
+** DELETE, but foreign key actions are not.
+*/
+void sqlite3FkDropTable(Parse *pParse, SrcList *pName, Table *pTab){
+  sqlite3 *db = pParse->db;
+  if( (db->flags&SQLITE_ForeignKeys) && !IsVirtual(pTab) && !pTab->pSelect ){
+    int iSkip = 0;
+    Vdbe *v = sqlite3GetVdbe(pParse);
+
+    assert( v );                  /* VDBE has already been allocated */
+    if( sqlite3FkReferences(pTab)==0 ){
+      /* Search for a deferred foreign key constraint for which this table
+      ** is the child table. If one cannot be found, return without 
+      ** generating any VDBE code. If one can be found, then jump over
+      ** the entire DELETE if there are no outstanding deferred constraints
+      ** when this statement is run.  */
+      FKey *p;
+      for(p=pTab->pFKey; p; p=p->pNextFrom){
+        if( p->isDeferred || (db->flags & SQLITE_DeferFKs) ) break;
+      }
+      if( !p ) return;
+      iSkip = sqlite3VdbeMakeLabel(v);
+      sqlite3VdbeAddOp2(v, OP_FkIfZero, 1, iSkip); VdbeCoverage(v);
+    }
+
+    pParse->disableTriggers = 1;
+    sqlite3DeleteFrom(pParse, sqlite3SrcListDup(db, pName, 0), 0);
+    pParse->disableTriggers = 0;
+
+    /* If the DELETE has generated immediate foreign key constraint 
+    ** violations, halt the VDBE and return an error at this point, before
+    ** any modifications to the schema are made. This is because statement
+    ** transactions are not able to rollback schema changes.  
+    **
+    ** If the SQLITE_DeferFKs flag is set, then this is not required, as
+    ** the statement transaction will not be rolled back even if FK
+    ** constraints are violated.
+    */
+    if( (db->flags & SQLITE_DeferFKs)==0 ){
+      sqlite3VdbeAddOp2(v, OP_FkIfZero, 0, sqlite3VdbeCurrentAddr(v)+2);
+      VdbeCoverage(v);
+      sqlite3HaltConstraint(pParse, SQLITE_CONSTRAINT_FOREIGNKEY,
+          OE_Abort, 0, P4_STATIC, P5_ConstraintFK);
+    }
+
+    if( iSkip ){
+      sqlite3VdbeResolveLabel(v, iSkip);
+    }
+  }
+}
+
+
+/*
+** The second argument points to an FKey object representing a foreign key
+** for which pTab is the child table. An UPDATE statement against pTab
+** is currently being processed. For each column of the table that is 
+** actually updated, the corresponding element in the aChange[] array
+** is zero or greater (if a column is unmodified the corresponding element
+** is set to -1). If the rowid column is modified by the UPDATE statement
+** the bChngRowid argument is non-zero.
+**
+** This function returns true if any of the columns that are part of the
+** child key for FK constraint *p are modified.
+*/
+static int fkChildIsModified(
+  Table *pTab,                    /* Table being updated */
+  FKey *p,                        /* Foreign key for which pTab is the child */
+  int *aChange,                   /* Array indicating modified columns */
+  int bChngRowid                  /* True if rowid is modified by this update */
+){
+  int i;
+  for(i=0; i<p->nCol; i++){
+    int iChildKey = p->aCol[i].iFrom;
+    if( aChange[iChildKey]>=0 ) return 1;
+    if( iChildKey==pTab->iPKey && bChngRowid ) return 1;
+  }
+  return 0;
+}
+
+/*
+** The second argument points to an FKey object representing a foreign key
+** for which pTab is the parent table. An UPDATE statement against pTab
+** is currently being processed. For each column of the table that is 
+** actually updated, the corresponding element in the aChange[] array
+** is zero or greater (if a column is unmodified the corresponding element
+** is set to -1). If the rowid column is modified by the UPDATE statement
+** the bChngRowid argument is non-zero.
+**
+** This function returns true if any of the columns that are part of the
+** parent key for FK constraint *p are modified.
+*/
+static int fkParentIsModified(
+  Table *pTab, 
+  FKey *p, 
+  int *aChange, 
+  int bChngRowid
+){
+  int i;
+  for(i=0; i<p->nCol; i++){
+    char *zKey = p->aCol[i].zCol;
+    int iKey;
+    for(iKey=0; iKey<pTab->nCol; iKey++){
+      if( aChange[iKey]>=0 || (iKey==pTab->iPKey && bChngRowid) ){
+        Column *pCol = &pTab->aCol[iKey];
+        if( zKey ){
+          if( 0==sqlite3StrICmp(pCol->zName, zKey) ) return 1;
+        }else if( pCol->colFlags & COLFLAG_PRIMKEY ){
+          return 1;
+        }
+      }
+    }
+  }
+  return 0;
+}
+
+/*
+** Return true if the parser passed as the first argument is being
+** used to code a trigger that is really a "SET NULL" action belonging
+** to trigger pFKey.
+*/
+static int isSetNullAction(Parse *pParse, FKey *pFKey){
+  Parse *pTop = sqlite3ParseToplevel(pParse);
+  if( pTop->pTriggerPrg ){
+    Trigger *p = pTop->pTriggerPrg->pTrigger;
+    if( (p==pFKey->apTrigger[0] && pFKey->aAction[0]==OE_SetNull)
+     || (p==pFKey->apTrigger[1] && pFKey->aAction[1]==OE_SetNull)
+    ){
+      return 1;
+    }
+  }
+  return 0;
+}
+
+/*
+** This function is called when inserting, deleting or updating a row of
+** table pTab to generate VDBE code to perform foreign key constraint 
+** processing for the operation.
+**
+** For a DELETE operation, parameter regOld is passed the index of the
+** first register in an array of (pTab->nCol+1) registers containing the
+** rowid of the row being deleted, followed by each of the column values
+** of the row being deleted, from left to right. Parameter regNew is passed
+** zero in this case.
+**
+** For an INSERT operation, regOld is passed zero and regNew is passed the
+** first register of an array of (pTab->nCol+1) registers containing the new
+** row data.
+**
+** For an UPDATE operation, this function is called twice. Once before
+** the original record is deleted from the table using the calling convention
+** described for DELETE. Then again after the original record is deleted
+** but before the new record is inserted using the INSERT convention. 
+*/
+void sqlite3FkCheck(
+  Parse *pParse,                  /* Parse context */
+  Table *pTab,                    /* Row is being deleted from this table */ 
+  int regOld,                     /* Previous row data is stored here */
+  int regNew,                     /* New row data is stored here */
+  int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
+  int bChngRowid                  /* True if rowid is UPDATEd */
+){
+  sqlite3 *db = pParse->db;       /* Database handle */
+  FKey *pFKey;                    /* Used to iterate through FKs */
+  int iDb;                        /* Index of database containing pTab */
+  const char *zDb;                /* Name of database containing pTab */
+  int isIgnoreErrors = pParse->disableTriggers;
+
+  /* Exactly one of regOld and regNew should be non-zero. */
+  assert( (regOld==0)!=(regNew==0) );
+
+  /* If foreign-keys are disabled, this function is a no-op. */
+  if( (db->flags&SQLITE_ForeignKeys)==0 ) return;
+
+  iDb = sqlite3SchemaToIndex(db, pTab->pSchema);
+  zDb = db->aDb[iDb].zDbSName;
+
+  /* Loop through all the foreign key constraints for which pTab is the
+  ** child table (the table that the foreign key definition is part of).  */
+  for(pFKey=pTab->pFKey; pFKey; pFKey=pFKey->pNextFrom){
+    Table *pTo;                   /* Parent table of foreign key pFKey */
+    Index *pIdx = 0;              /* Index on key columns in pTo */
+    int *aiFree = 0;
+    int *aiCol;
+    int iCol;
+    int i;
+    int bIgnore = 0;
+
+    if( aChange 
+     && sqlite3_stricmp(pTab->zName, pFKey->zTo)!=0
+     && fkChildIsModified(pTab, pFKey, aChange, bChngRowid)==0 
+    ){
+      continue;
+    }
+
+    /* Find the parent table of this foreign key. Also find a unique index 
+    ** on the parent key columns in the parent table. If either of these 
+    ** schema items cannot be located, set an error in pParse and return 
+    ** early.  */
+    if( pParse->disableTriggers ){
+      pTo = sqlite3FindTable(db, pFKey->zTo, zDb);
+    }else{
+      pTo = sqlite3LocateTable(pParse, 0, pFKey->zTo, zDb);
+    }
+    if( !pTo || sqlite3FkLocateIndex(pParse, pTo, pFKey, &pIdx, &aiFree) ){
+      assert( isIgnoreErrors==0 || (regOld!=0 && regNew==0) );
+      if( !isIgnoreErrors || db->mallocFailed ) return;
+      if( pTo==0 ){
+        /* If isIgnoreErrors is true, then a table is being dropped. In this
+        ** case SQLite runs a "DELETE FROM xxx" on the table being dropped
+        ** before actually dropping it in order to check FK constraints.
+        ** If the parent table of an FK constraint on the current table is
+        ** missing, behave as if it is empty. i.e. decrement the relevant
+        ** FK counter for each row of the current table with non-NULL keys.
+        */
+        Vdbe *v = sqlite3GetVdbe(pParse);
+        int iJump = sqlite3VdbeCurrentAddr(v) + pFKey->nCol + 1;
+        for(i=0; i<pFKey->nCol; i++){
+          int iReg = pFKey->aCol[i].iFrom + regOld + 1;
+          sqlite3VdbeAddOp2(v, OP_IsNull, iReg, iJump); VdbeCoverage(v);
+        }
+        sqlite3VdbeAddOp2(v, OP_FkCounter, pFKey->isDeferred, -1);
+      }
+      continue;
+    }
+    assert( pFKey->nCol==1 || (aiFree && pIdx) );
+
+    if( aiFree ){
+      aiCol = aiFree;
+    }else{
+      iCol = pFKey->aCol[0].iFrom;
+      aiCol = &iCol;
+    }
+    for(i=0; i<pFKey->nCol; i++){
+      if( aiCol[i]==pTab->iPKey ){
+        aiCol[i] = -1;
+      }
+      assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
+#ifndef SQLITE_OMIT_AUTHORIZATION
+      /* Request permission to read the parent key columns. If the 
+      ** authorization callback returns SQLITE_IGNORE, behave as if any
+      ** values read from the parent table are NULL. */
+      if( db->xAuth ){
+        int rcauth;
+        char *zCol = pTo->aCol[pIdx ? pIdx->aiColumn[i] : pTo->iPKey].zName;
+        rcauth = sqlite3AuthReadCol(pParse, pTo->zName, zCol, iDb);
+        bIgnore = (rcauth==SQLITE_IGNORE);
+      }
+#endif
+    }
+
+    /* Take a shared-cache advisory read-lock on the parent table. Allocate 
+    ** a cursor to use to search the unique index on the parent key columns 
+    ** in the parent table.  */
+    sqlite3TableLock(pParse, iDb, pTo->tnum, 0, pTo->zName);
+    pParse->nTab++;
+
+    if( regOld!=0 ){
+      /* A row is being removed from the child table. Search for the parent.
+      ** If the parent does not exist, removing the child row resolves an 
+      ** outstanding foreign key constraint violation. */
+      fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regOld, -1, bIgnore);
+    }
+    if( regNew!=0 && !isSetNullAction(pParse, pFKey) ){
+      /* A row is being added to the child table. If a parent row cannot
+      ** be found, adding the child row has violated the FK constraint. 
+      **
+      ** If this operation is being performed as part of a trigger program
+      ** that is actually a "SET NULL" action belonging to this very 
+      ** foreign key, then omit this scan altogether. As all child key
+      ** values are guaranteed to be NULL, it is not possible for adding
+      ** this row to cause an FK violation.  */
+      fkLookupParent(pParse, iDb, pTo, pIdx, pFKey, aiCol, regNew, +1, bIgnore);
+    }
+
+    sqlite3DbFree(db, aiFree);
+  }
+
+  /* Loop through all the foreign key constraints that refer to this table.
+  ** (the "child" constraints) */
+  for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
+    Index *pIdx = 0;              /* Foreign key index for pFKey */
+    SrcList *pSrc;
+    int *aiCol = 0;
+
+    if( aChange && fkParentIsModified(pTab, pFKey, aChange, bChngRowid)==0 ){
+      continue;
+    }
+
+    if( !pFKey->isDeferred && !(db->flags & SQLITE_DeferFKs) 
+     && !pParse->pToplevel && !pParse->isMultiWrite 
+    ){
+      assert( regOld==0 && regNew!=0 );
+      /* Inserting a single row into a parent table cannot cause (or fix)
+      ** an immediate foreign key violation. So do nothing in this case.  */
+      continue;
+    }
+
+    if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ){
+      if( !isIgnoreErrors || db->mallocFailed ) return;
+      continue;
+    }
+    assert( aiCol || pFKey->nCol==1 );
+
+    /* Create a SrcList structure containing the child table.  We need the
+    ** child table as a SrcList for sqlite3WhereBegin() */
+    pSrc = sqlite3SrcListAppend(db, 0, 0, 0);
+    if( pSrc ){
+      struct SrcList_item *pItem = pSrc->a;
+      pItem->pTab = pFKey->pFrom;
+      pItem->zName = pFKey->pFrom->zName;
+      pItem->pTab->nTabRef++;
+      pItem->iCursor = pParse->nTab++;
+  
+      if( regNew!=0 ){
+        fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regNew, -1);
+      }
+      if( regOld!=0 ){
+        int eAction = pFKey->aAction[aChange!=0];
+        fkScanChildren(pParse, pSrc, pTab, pIdx, pFKey, aiCol, regOld, 1);
+        /* If this is a deferred FK constraint, or a CASCADE or SET NULL
+        ** action applies, then any foreign key violations caused by
+        ** removing the parent key will be rectified by the action trigger.
+        ** So do not set the "may-abort" flag in this case.
+        **
+        ** Note 1: If the FK is declared "ON UPDATE CASCADE", then the
+        ** may-abort flag will eventually be set on this statement anyway
+        ** (when this function is called as part of processing the UPDATE
+        ** within the action trigger).
+        **
+        ** Note 2: At first glance it may seem like SQLite could simply omit
+        ** all OP_FkCounter related scans when either CASCADE or SET NULL
+        ** applies. The trouble starts if the CASCADE or SET NULL action 
+        ** trigger causes other triggers or action rules attached to the 
+        ** child table to fire. In these cases the fk constraint counters
+        ** might be set incorrectly if any OP_FkCounter related scans are 
+        ** omitted.  */
+        if( !pFKey->isDeferred && eAction!=OE_Cascade && eAction!=OE_SetNull ){
+          sqlite3MayAbort(pParse);
+        }
+      }
+      pItem->zName = 0;
+      sqlite3SrcListDelete(db, pSrc);
+    }
+    sqlite3DbFree(db, aiCol);
+  }
+}
+
+#define COLUMN_MASK(x) (((x)>31) ? 0xffffffff : ((u32)1<<(x)))
+
+/*
+** This function is called before generating code to update or delete a 
+** row contained in table pTab.
+*/
+u32 sqlite3FkOldmask(
+  Parse *pParse,                  /* Parse context */
+  Table *pTab                     /* Table being modified */
+){
+  u32 mask = 0;
+  if( pParse->db->flags&SQLITE_ForeignKeys ){
+    FKey *p;
+    int i;
+    for(p=pTab->pFKey; p; p=p->pNextFrom){
+      for(i=0; i<p->nCol; i++) mask |= COLUMN_MASK(p->aCol[i].iFrom);
+    }
+    for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
+      Index *pIdx = 0;
+      sqlite3FkLocateIndex(pParse, pTab, p, &pIdx, 0);
+      if( pIdx ){
+        for(i=0; i<pIdx->nKeyCol; i++){
+          assert( pIdx->aiColumn[i]>=0 );
+          mask |= COLUMN_MASK(pIdx->aiColumn[i]);
+        }
+      }
+    }
+  }
+  return mask;
+}
+
+
+/*
+** This function is called before generating code to update or delete a 
+** row contained in table pTab. If the operation is a DELETE, then
+** parameter aChange is passed a NULL value. For an UPDATE, aChange points
+** to an array of size N, where N is the number of columns in table pTab.
+** If the i'th column is not modified by the UPDATE, then the corresponding 
+** entry in the aChange[] array is set to -1. If the column is modified,
+** the value is 0 or greater. Parameter chngRowid is set to true if the
+** UPDATE statement modifies the rowid fields of the table.
+**
+** If any foreign key processing will be required, this function returns
+** true. If there is no foreign key related processing, this function 
+** returns false.
+*/
+int sqlite3FkRequired(
+  Parse *pParse,                  /* Parse context */
+  Table *pTab,                    /* Table being modified */
+  int *aChange,                   /* Non-NULL for UPDATE operations */
+  int chngRowid                   /* True for UPDATE that affects rowid */
+){
+  if( pParse->db->flags&SQLITE_ForeignKeys ){
+    if( !aChange ){
+      /* A DELETE operation. Foreign key processing is required if the 
+      ** table in question is either the child or parent table for any 
+      ** foreign key constraint.  */
+      return (sqlite3FkReferences(pTab) || pTab->pFKey);
+    }else{
+      /* This is an UPDATE. Foreign key processing is only required if the
+      ** operation modifies one or more child or parent key columns. */
+      FKey *p;
+
+      /* Check if any child key columns are being modified. */
+      for(p=pTab->pFKey; p; p=p->pNextFrom){
+        if( fkChildIsModified(pTab, p, aChange, chngRowid) ) return 1;
+      }
+
+      /* Check if any parent key columns are being modified. */
+      for(p=sqlite3FkReferences(pTab); p; p=p->pNextTo){
+        if( fkParentIsModified(pTab, p, aChange, chngRowid) ) return 1;
+      }
+    }
+  }
+  return 0;
+}
+
+/*
+** This function is called when an UPDATE or DELETE operation is being 
+** compiled on table pTab, which is the parent table of foreign-key pFKey.
+** If the current operation is an UPDATE, then the pChanges parameter is
+** passed a pointer to the list of columns being modified. If it is a
+** DELETE, pChanges is passed a NULL pointer.
+**
+** It returns a pointer to a Trigger structure containing a trigger
+** equivalent to the ON UPDATE or ON DELETE action specified by pFKey.
+** If the action is "NO ACTION" or "RESTRICT", then a NULL pointer is
+** returned (these actions require no special handling by the triggers
+** sub-system, code for them is created by fkScanChildren()).
+**
+** For example, if pFKey is the foreign key and pTab is table "p" in 
+** the following schema:
+**
+**   CREATE TABLE p(pk PRIMARY KEY);
+**   CREATE TABLE c(ck REFERENCES p ON DELETE CASCADE);
+**
+** then the returned trigger structure is equivalent to:
+**
+**   CREATE TRIGGER ... DELETE ON p BEGIN
+**     DELETE FROM c WHERE ck = old.pk;
+**   END;
+**
+** The returned pointer is cached as part of the foreign key object. It
+** is eventually freed along with the rest of the foreign key object by 
+** sqlite3FkDelete().
+*/
+static Trigger *fkActionTrigger(
+  Parse *pParse,                  /* Parse context */
+  Table *pTab,                    /* Table being updated or deleted from */
+  FKey *pFKey,                    /* Foreign key to get action for */
+  ExprList *pChanges              /* Change-list for UPDATE, NULL for DELETE */
+){
+  sqlite3 *db = pParse->db;       /* Database handle */
+  int action;                     /* One of OE_None, OE_Cascade etc. */
+  Trigger *pTrigger;              /* Trigger definition to return */
+  int iAction = (pChanges!=0);    /* 1 for UPDATE, 0 for DELETE */
+
+  action = pFKey->aAction[iAction];
+  if( action==OE_Restrict && (db->flags & SQLITE_DeferFKs) ){
+    return 0;
+  }
+  pTrigger = pFKey->apTrigger[iAction];
+
+  if( action!=OE_None && !pTrigger ){
+    char const *zFrom;            /* Name of child table */
+    int nFrom;                    /* Length in bytes of zFrom */
+    Index *pIdx = 0;              /* Parent key index for this FK */
+    int *aiCol = 0;               /* child table cols -> parent key cols */
+    TriggerStep *pStep = 0;        /* First (only) step of trigger program */
+    Expr *pWhere = 0;             /* WHERE clause of trigger step */
+    ExprList *pList = 0;          /* Changes list if ON UPDATE CASCADE */
+    Select *pSelect = 0;          /* If RESTRICT, "SELECT RAISE(...)" */
+    int i;                        /* Iterator variable */
+    Expr *pWhen = 0;              /* WHEN clause for the trigger */
+
+    if( sqlite3FkLocateIndex(pParse, pTab, pFKey, &pIdx, &aiCol) ) return 0;
+    assert( aiCol || pFKey->nCol==1 );
+
+    for(i=0; i<pFKey->nCol; i++){
+      Token tOld = { "old", 3 };  /* Literal "old" token */
+      Token tNew = { "new", 3 };  /* Literal "new" token */
+      Token tFromCol;             /* Name of column in child table */
+      Token tToCol;               /* Name of column in parent table */
+      int iFromCol;               /* Idx of column in child table */
+      Expr *pEq;                  /* tFromCol = OLD.tToCol */
+
+      iFromCol = aiCol ? aiCol[i] : pFKey->aCol[0].iFrom;
+      assert( iFromCol>=0 );
+      assert( pIdx!=0 || (pTab->iPKey>=0 && pTab->iPKey<pTab->nCol) );
+      assert( pIdx==0 || pIdx->aiColumn[i]>=0 );
+      sqlite3TokenInit(&tToCol,
+                   pTab->aCol[pIdx ? pIdx->aiColumn[i] : pTab->iPKey].zName);
+      sqlite3TokenInit(&tFromCol, pFKey->pFrom->aCol[iFromCol].zName);
+
+      /* Create the expression "OLD.zToCol = zFromCol". It is important
+      ** that the "OLD.zToCol" term is on the LHS of the = operator, so
+      ** that the affinity and collation sequence associated with the
+      ** parent table are used for the comparison. */
+      pEq = sqlite3PExpr(pParse, TK_EQ,
+          sqlite3PExpr(pParse, TK_DOT, 
+            sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
+            sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
+          sqlite3ExprAlloc(db, TK_ID, &tFromCol, 0)
+      );
+      pWhere = sqlite3ExprAnd(db, pWhere, pEq);
+
+      /* For ON UPDATE, construct the next term of the WHEN clause.
+      ** The final WHEN clause will be like this:
+      **
+      **    WHEN NOT(old.col1 IS new.col1 AND ... AND old.colN IS new.colN)
+      */
+      if( pChanges ){
+        pEq = sqlite3PExpr(pParse, TK_IS,
+            sqlite3PExpr(pParse, TK_DOT, 
+              sqlite3ExprAlloc(db, TK_ID, &tOld, 0),
+              sqlite3ExprAlloc(db, TK_ID, &tToCol, 0)),
+            sqlite3PExpr(pParse, TK_DOT, 
+              sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
+              sqlite3ExprAlloc(db, TK_ID, &tToCol, 0))
+            );
+        pWhen = sqlite3ExprAnd(db, pWhen, pEq);
+      }
+  
+      if( action!=OE_Restrict && (action!=OE_Cascade || pChanges) ){
+        Expr *pNew;
+        if( action==OE_Cascade ){
+          pNew = sqlite3PExpr(pParse, TK_DOT, 
+            sqlite3ExprAlloc(db, TK_ID, &tNew, 0),
+            sqlite3ExprAlloc(db, TK_ID, &tToCol, 0));
+        }else if( action==OE_SetDflt ){
+          Expr *pDflt = pFKey->pFrom->aCol[iFromCol].pDflt;
+          if( pDflt ){
+            pNew = sqlite3ExprDup(db, pDflt, 0);
+          }else{
+            pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
+          }
+        }else{
+          pNew = sqlite3ExprAlloc(db, TK_NULL, 0, 0);
+        }
+        pList = sqlite3ExprListAppend(pParse, pList, pNew);
+        sqlite3ExprListSetName(pParse, pList, &tFromCol, 0);
+      }
+    }
+    sqlite3DbFree(db, aiCol);
+
+    zFrom = pFKey->pFrom->zName;
+    nFrom = sqlite3Strlen30(zFrom);
+
+    if( action==OE_Restrict ){
+      Token tFrom;
+      Expr *pRaise; 
+
+      tFrom.z = zFrom;
+      tFrom.n = nFrom;
+      pRaise = sqlite3Expr(db, TK_RAISE, "FOREIGN KEY constraint failed");
+      if( pRaise ){
+        pRaise->affinity = OE_Abort;
+      }
+      pSelect = sqlite3SelectNew(pParse, 
+          sqlite3ExprListAppend(pParse, 0, pRaise),
+          sqlite3SrcListAppend(db, 0, &tFrom, 0),
+          pWhere,
+          0, 0, 0, 0, 0, 0
+      );
+      pWhere = 0;
+    }
+
+    /* Disable lookaside memory allocation */
+    db->lookaside.bDisable++;
+
+    pTrigger = (Trigger *)sqlite3DbMallocZero(db, 
+        sizeof(Trigger) +         /* struct Trigger */
+        sizeof(TriggerStep) +     /* Single step in trigger program */
+        nFrom + 1                 /* Space for pStep->zTarget */
+    );
+    if( pTrigger ){
+      pStep = pTrigger->step_list = (TriggerStep *)&pTrigger[1];
+      pStep->zTarget = (char *)&pStep[1];
+      memcpy((char *)pStep->zTarget, zFrom, nFrom);
+  
+      pStep->pWhere = sqlite3ExprDup(db, pWhere, EXPRDUP_REDUCE);
+      pStep->pExprList = sqlite3ExprListDup(db, pList, EXPRDUP_REDUCE);
+      pStep->pSelect = sqlite3SelectDup(db, pSelect, EXPRDUP_REDUCE);
+      if( pWhen ){
+        pWhen = sqlite3PExpr(pParse, TK_NOT, pWhen, 0);
+        pTrigger->pWhen = sqlite3ExprDup(db, pWhen, EXPRDUP_REDUCE);
+      }
+    }
+
+    /* Re-enable the lookaside buffer, if it was disabled earlier. */
+    db->lookaside.bDisable--;
+
+    sqlite3ExprDelete(db, pWhere);
+    sqlite3ExprDelete(db, pWhen);
+    sqlite3ExprListDelete(db, pList);
+    sqlite3SelectDelete(db, pSelect);
+    if( db->mallocFailed==1 ){
+      fkTriggerDelete(db, pTrigger);
+      return 0;
+    }
+    assert( pStep!=0 );
+
+    switch( action ){
+      case OE_Restrict:
+        pStep->op = TK_SELECT; 
+        break;
+      case OE_Cascade: 
+        if( !pChanges ){ 
+          pStep->op = TK_DELETE; 
+          break; 
+        }
+      default:
+        pStep->op = TK_UPDATE;
+    }
+    pStep->pTrig = pTrigger;
+    pTrigger->pSchema = pTab->pSchema;
+    pTrigger->pTabSchema = pTab->pSchema;
+    pFKey->apTrigger[iAction] = pTrigger;
+    pTrigger->op = (pChanges ? TK_UPDATE : TK_DELETE);
+  }
+
+  return pTrigger;
+}
+
+/*
+** This function is called when deleting or updating a row to implement
+** any required CASCADE, SET NULL or SET DEFAULT actions.
+*/
+void sqlite3FkActions(
+  Parse *pParse,                  /* Parse context */
+  Table *pTab,                    /* Table being updated or deleted from */
+  ExprList *pChanges,             /* Change-list for UPDATE, NULL for DELETE */
+  int regOld,                     /* Address of array containing old row */
+  int *aChange,                   /* Array indicating UPDATEd columns (or 0) */
+  int bChngRowid                  /* True if rowid is UPDATEd */
+){
+  /* If foreign-key support is enabled, iterate through all FKs that 
+  ** refer to table pTab. If there is an action associated with the FK 
+  ** for this operation (either update or delete), invoke the associated 
+  ** trigger sub-program.  */
+  if( pParse->db->flags&SQLITE_ForeignKeys ){
+    FKey *pFKey;                  /* Iterator variable */
+    for(pFKey = sqlite3FkReferences(pTab); pFKey; pFKey=pFKey->pNextTo){
+      if( aChange==0 || fkParentIsModified(pTab, pFKey, aChange, bChngRowid) ){
+        Trigger *pAct = fkActionTrigger(pParse, pTab, pFKey, pChanges);
+        if( pAct ){
+          sqlite3CodeRowTriggerDirect(pParse, pAct, pTab, regOld, OE_Abort, 0);
+        }
+      }
+    }
+  }
+}
+
+#endif /* ifndef SQLITE_OMIT_TRIGGER */
+
+/*
+** Free all memory associated with foreign key definitions attached to
+** table pTab. Remove the deleted foreign keys from the Schema.fkeyHash
+** hash table.
+*/
+void sqlite3FkDelete(sqlite3 *db, Table *pTab){
+  FKey *pFKey;                    /* Iterator variable */
+  FKey *pNext;                    /* Copy of pFKey->pNextFrom */
+
+  assert( db==0 || IsVirtual(pTab)
+         || sqlite3SchemaMutexHeld(db, 0, pTab->pSchema) );
+  for(pFKey=pTab->pFKey; pFKey; pFKey=pNext){
+
+    /* Remove the FK from the fkeyHash hash table. */
+    if( !db || db->pnBytesFreed==0 ){
+      if( pFKey->pPrevTo ){
+        pFKey->pPrevTo->pNextTo = pFKey->pNextTo;
+      }else{
+        void *p = (void *)pFKey->pNextTo;
+        const char *z = (p ? pFKey->pNextTo->zTo : pFKey->zTo);
+        sqlite3HashInsert(&pTab->pSchema->fkeyHash, z, p);
+      }
+      if( pFKey->pNextTo ){
+        pFKey->pNextTo->pPrevTo = pFKey->pPrevTo;
+      }
+    }
+
+    /* EV: R-30323-21917 Each foreign key constraint in SQLite is
+    ** classified as either immediate or deferred.
+    */
+    assert( pFKey->isDeferred==0 || pFKey->isDeferred==1 );
+
+    /* Delete any triggers created to implement actions for this FK. */
+#ifndef SQLITE_OMIT_TRIGGER
+    fkTriggerDelete(db, pFKey->apTrigger[0]);
+    fkTriggerDelete(db, pFKey->apTrigger[1]);
+#endif
+
+    pNext = pFKey->pNextFrom;
+    sqlite3DbFree(db, pFKey);
+  }
+}
+#endif /* ifndef SQLITE_OMIT_FOREIGN_KEY */