[sql] Import reference version of SQLite 3.8.7.4.

third_party/sqlite/sqlite-src-3080704/README.md

+<h1 align="center">SQLite Source Repository</h1>
+
+This repository contains the complete source code for the SQLite database
+engine.  Some test scripts are also include.  However, many other test scripts
+and most of the documentation are managed separately.
+
+## Compiling
+
+First create a directory in which to place
+the build products.  It is recommended, but not required, that the
+build directory be separate from the source directory.  Cd into the
+build directory and then from the build directory run the configure
+script found at the root of the source tree.  Then run "make".
+
+For example:
+
+    tar xzf sqlite.tar.gz    ;#  Unpack the source tree into "sqlite"
+    mkdir bld                ;#  Build will occur in a sibling directory
+    cd bld                   ;#  Change to the build directory
+    ../sqlite/configure      ;#  Run the configure script
+    make                     ;#  Run the makefile.
+    make sqlite3.c           ;#  Build the "amalgamation" source file
+    make test                ;#  Run some tests (requires Tcl)
+
+See the makefile for additional targets.
+
+The configure script uses autoconf 2.61 and libtool.  If the configure
+script does not work out for you, there is a generic makefile named
+"Makefile.linux-gcc" in the top directory of the source tree that you
+can copy and edit to suit your needs.  Comments on the generic makefile
+show what changes are needed.
+
+## Using MSVC
+
+On Windows, all applicable build products can be compiled with MSVC.
+First open the command prompt window associated with the desired compiler
+version (e.g. "Developer Command Prompt for VS2013").  Next, use NMAKE
+with the provided "Makefile.msc" to build one of the supported targets.
+
+For example:
+
+    mkdir bld
+    cd bld
+    nmake /f Makefile.msc TOP=..\sqlite
+    nmake /f Makefile.msc sqlite3.c TOP=..\sqlite
+    nmake /f Makefile.msc sqlite3.dll TOP=..\sqlite
+    nmake /f Makefile.msc sqlite3.exe TOP=..\sqlite
+    nmake /f Makefile.msc test TOP=..\sqlite
+
+There are several build options that can be set via the NMAKE command
+line.  For example, to build for WinRT, simply add "FOR_WINRT=1" argument
+to the "sqlite3.dll" command line above.  When debugging into the SQLite
+code, adding the "DEBUG=1" argument to one of the above command lines is
+recommended.
+
+SQLite does not require Tcl to run, but a Tcl installation is required
+by the makefiles (including those for MSVC).  SQLite contains a lot of
+generated code and Tcl is used to do much of that code generation.  The
+makefiles also require AWK.
+
+## Source Code Tour
+
+Most of the core source files are in the **src/** subdirectory.  But
+src/ also contains files used to build the "testfixture" test harness;
+those file all begin with "test".  And src/ contains the "shell.c" file
+which is the main program for the "sqlite3.exe" command-line shell and
+the "tclsqlite.c" file which implements the bindings to SQLite from the
+Tcl programming language.  (Historical note:  SQLite began as a Tcl
+extension and only later escaped to the wild as an independent library.)
+
+Test scripts and programs are found in the **test/** subdirectory.
+There are other test suites for SQLite (see
+[How SQLite Is Tested](http://www.sqlite.org/testing.html))
+but those other test suites are
+in separate source repositories.
+
+The **ext/** subdirectory contains code for extensions.  The
+Full-text search engine is in **ext/fts3**.  The R-Tree engine is in
+**ext/rtree**.  The **ext/misc** subdirectory contains a number of
+smaller, single-file extensions, such as a REGEXP operator.
+
+The **tool/** subdirectory contains various scripts and programs used
+for building generated source code files or for testing or for generating
+accessory programs such as "sqlite3_analyzer(.exe)".
+
+### Generated Source Code Files
+
+Several of the C-language source files used by SQLite are generated from
+other sources rather than being typed in manually by a programmer.  This
+section will summarize those automatically-generated files.  To create all
+of the automatically-generated files, simply run "make target&#95;source".
+The "target&#95;source" make target will create a subdirectory "tsrc/" and
+fill it with all the source files needed to build SQLite, both
+manually-edited files and automatically-generated files.
+
+The SQLite interface is defined by the **sqlite3.h** header file, which is
+generated from src/sqlite.h.in, ./manifest.uuid, and ./VERSION.  The
+Tcl script at tool/mksqlite3h.tcl does the conversion.  The manifest.uuid
+file contains the SHA1 hash of the particular check-in and is used to generate
+the SQLITE_SOURCE_ID macro.  The VERSION file contains the current SQLite
+version number.  The sqlite3.h header is really just a copy of src/sqlite.h.in
+with the source-id and version number inserted at just the right spots.
+Note that comment text in the sqlite3.h file is used to generate much of
+the SQLite API documentation.  The Tcl scripts used to generate that
+documentation are in a separate source repository.
+
+The SQL language parser is **parse.c** which is generate from a grammar in
+the src/parse.y file.  The conversion of "parse.y" into "parse.c" is done
+by the [lemon](./doc/lemon.html) LALR(1) parser generator.  The source code
+for lemon is at tool/lemon.c.  Lemon uses a
+template for generating its parser.  A generic template is in tool/lempar.c,
+but SQLite uses a slightly modified template found in src/lempar.c.
+
+Lemon also generates the **parse.h** header file, at the same time it
+generates parse.c. But the parse.h header file is
+modified further (to add additional symbols) using the ./addopcodes.awk
+AWK script.
+
+The **opcodes.h** header file contains macros that define the numbers
+corresponding to opcodes in the "VDBE" virtual machine.  The opcodes.h
+file is generated by the scanning the src/vdbe.c source file.  The
+AWK script at ./mkopcodeh.awk does this scan and generates opcodes.h.
+A second AWK script, ./mkopcodec.awk, then scans opcodes.h to generate
+the **opcodes.c** source file, which contains a reverse mapping from
+opcode-number to opcode-name that is used for EXPLAIN output.
+
+The **keywordhash.h** header file contains the definition of a hash table
+that maps SQL language keywords (ex: "CREATE", "SELECT", "INDEX", etc.) into
+the numeric codes used by the parse.c parser.  The keywordhash.h file is
+generated by a C-language program at tool mkkeywordhash.c.
+
+### The Amalgamation
+
+All of the individual C source code and header files (both manually-edited
+and automatically-generated) can be combined into a single big source file
+**sqlite3.c** called "the amalgamation".  The amalgamation is the recommended
+way of using SQLite in a larger application.  Combining all individual
+source code files into a single big source code file allows the C compiler
+to perform more cross-procedure analysis and generate better code.  SQLite
+runs about 5% faster when compiled from the amalgamation versus when compiled
+from individual source files.
+
+The amalgamation is generated from the tool/mksqlite3c.tcl Tcl script.
+First, all of the individual source files must be gathered into the tsrc/
+subdirectory (using the equivalent of "make target_source") then the
+tool/mksqlite3c.tcl script is run to copy them all together in just the
+right order while resolving internal "#include" references.
+
+The amalgamation source file is more than 100K lines long.  Some symbolic
+debuggers (most notably MSVC) are unable to deal with files longer than 64K
+lines.  To work around this, a separate Tcl script, tool/split-sqlite3c.tcl,
+can be run on the amalgamation to break it up into a single small C file
+called **sqlite3-all.c** that does #include on about five other files
+named **sqlite3-1.c**, **sqlite3-2.c**, ..., **sqlite3-5.c**.  In this way,
+all of the source code is contained within a single translation unit so
+that the compiler can do extra cross-procedure optimization, but no
+individual source file exceeds 32K lines in length.
+
+## How It All Fits Together
+
+SQLite is modular in design.
+See the [architectural description](http://www.sqlite.org/arch.html)
+for details. Other documents that are useful in
+(helping to understand how SQLite works include the
+[file format](http://www.sqlite.org/fileformat2.html) description,
+the [virtual machine](http://www.sqlite.org/vdbe.html) that runs
+prepared statements, the description of
+[how transactions work](http://www.sqlite.org/atomiccommit.html), and
+the [overview of the query planner](http://www.sqlite.org/optoverview.html).
+
+Unfortunately, years of effort have gone into optimizating SQLite, both
+for small size and high performance.  And optimizations tend to result in
+complex code.  So there is a lot of complexity in the SQLite implementation.
+
+Key files:
+
+  *  **sqlite3.h** - This file defines the public interface to the SQLite
+     library.  Readers will need to be familiar with this interface before
+     trying to understand how the library works internally.
+
+  *  **sqliteInt.h** - this header file defines many of the data objects
+     used internally by SQLite.
+
+  *  **parse.y** - This file describes the LALR(1) grammer that SQLite uses
+     to parse SQL statements, and the actions that are taken at each stop
+     in the parsing process.
+
+  *  **vdbe.c** - This file implements the virtual machine that runs
+     prepared statements.  There are various helper files whose names
+     begin with "vdbe".  The VDBE has access to the vdbeInt.h header file
+     which defines internal data objects.  The rest of SQLite interacts
+     with the VDBE through an interface defined by vdbe.h.
+
+  *  **where.c** - This file analyzes the WHERE clause and generates
+     virtual machine code to run queries efficiently.  This file is
+     sometimes called the "query optimizer".  It has its own private
+     header file, whereInt.h, that defines data objects used internally.
+
+  *  **btree.c** - This file contains the implementation of the B-Tree
+     storage engine used by SQLite.
+
+  *  **pager.c** - This file contains the "pager" implementation, the
+     module that implements transactions.
+
+  *  **os_unix.c** and **os_win.c** - These two files implement the interface
+     between SQLite and the underlying operating system using the run-time
+     pluggable VFS interface.
+
+
+## Contacts
+
+The main SQLite webpage is [http://www.sqlite.org/](http://www.sqlite.org/)
+with geographically distributed backup servers at
+[http://www2.sqlite.org/](http://www2.sqlite.org) and
+[http://www3.sqlite.org/](http://www3.sqlite.org).