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-1. OVERVIEW |
- |
- This README file describes the syntax of the arguments that may be passed to |
- the FTS3 MATCH operator used for full-text queries. For example, if table |
- "t1" is an Fts3 virtual table, the following SQL query: |
- |
- SELECT * FROM t1 WHERE <col> MATCH <full-text query> |
- |
- may be used to retrieve all rows that match a specified for full-text query. |
- The text "<col>" should be replaced by either the name of the fts3 table |
- (in this case "t1"), or by the name of one of the columns of the fts3 |
- table. <full-text-query> should be replaced by an SQL expression that |
- computes to a string containing an Fts3 query. |
- |
- If the left-hand-side of the MATCH operator is set to the name of the |
- fts3 table, then by default the query may be matched against any column |
- of the table. If it is set to a column name, then by default the query |
- may only match the specified column. In both cases this may be overriden |
- as part of the query text (see sections 2 and 3 below). |
- |
- As of SQLite version 3.6.8, Fts3 supports two slightly different query |
- formats; the standard syntax, which is used by default, and the enhanced |
- query syntax which can be selected by compiling with the pre-processor |
- symbol SQLITE_ENABLE_FTS3_PARENTHESIS defined. |
- |
- -DSQLITE_ENABLE_FTS3_PARENTHESIS |
- |
-2. STANDARD QUERY SYNTAX |
- |
- When using the standard Fts3 query syntax, a query usually consists of a |
- list of terms (words) separated by white-space characters. To match a |
- query, a row (or column) of an Fts3 table must contain each of the specified |
- terms. For example, the following query: |
- |
- <col> MATCH 'hello world' |
- |
- matches rows (or columns, if <col> is the name of a column name) that |
- contain at least one instance of the token "hello", and at least one |
- instance of the token "world". Tokens may be grouped into phrases using |
- quotation marks. In this case, a matching row or column must contain each |
- of the tokens in the phrase in the order specified, with no intervening |
- tokens. For example, the query: |
- |
- <col> MATCH '"hello world" joe" |
- |
- matches the first of the following two documents, but not the second or |
- third: |
- |
- "'Hello world', said Joe." |
- "One should always greet the world with a cheery hello, thought Joe." |
- "How many hello world programs could their be?" |
- |
- As well as grouping tokens together by phrase, the binary NEAR operator |
- may be used to search for rows that contain two or more specified tokens |
- or phrases within a specified proximity of each other. The NEAR operator |
- must always be specified in upper case. The word "near" in lower or mixed |
- case is treated as an ordinary token. For example, the following query: |
- |
- <col> MATCH 'engineering NEAR consultancy' |
- |
- matches rows that contain both the "engineering" and "consultancy" tokens |
- in the same column with not more than 10 other words between them. It does |
- not matter which of the two terms occurs first in the document, only that |
- they be seperated by only 10 tokens or less. The user may also specify |
- a different required proximity by adding "/N" immediately after the NEAR |
- operator, where N is an integer. For example: |
- |
- <col> MATCH 'engineering NEAR/5 consultancy' |
- |
- searches for a row containing an instance of each specified token seperated |
- by not more than 5 other tokens. More than one NEAR operator can be used |
- in as sequence. For example this query: |
- |
- <col> MATCH 'reliable NEAR/2 engineering NEAR/5 consultancy' |
- |
- searches for a row that contains an instance of the token "reliable" |
- seperated by not more than two tokens from an instance of "engineering", |
- which is in turn separated by not more than 5 other tokens from an |
- instance of the term "consultancy". Phrases enclosed in quotes may |
- also be used as arguments to the NEAR operator. |
- |
- Similar to the NEAR operator, one or more tokens or phrases may be |
- separated by OR operators. In this case, only one of the specified tokens |
- or phrases must appear in the document. For example, the query: |
- |
- <col> MATCH 'hello OR world' |
- |
- matches rows that contain either the term "hello", or the term "world", |
- or both. Note that unlike in many programming languages, the OR operator |
- has a higher precedence than the AND operators implied between white-space |
- separated tokens. The following query matches documents that contain the |
- term 'sqlite' and at least one of the terms 'fantastic' or 'impressive', |
- not those that contain both 'sqlite' and 'fantastic' or 'impressive': |
- |
- <col> MATCH 'sqlite fantastic OR impressive' |
- |
- Any token that is part of an Fts3 query expression, whether or not it is |
- part of a phrase enclosed in quotes, may have a '*' character appended to |
- it. In this case, the token matches all terms that begin with the characters |
- of the token, not just those that exactly match it. For example, the |
- following query: |
- |
- <col> MATCH 'sql*' |
- |
- matches all rows that contain the term "SQLite", as well as those that |
- contain "SQL". |
- |
- A token that is not part of a quoted phrase may be preceded by a '-' |
- character, which indicates that matching rows must not contain the |
- specified term. For example, the following: |
- |
- <col> MATCH '"database engine" -sqlite' |
- |
- matches rows that contain the phrase "database engine" but do not contain |
- the term "sqlite". If the '-' character occurs inside a quoted phrase, |
- it is ignored. It is possible to use both the '-' prefix and the '*' postfix |
- on a single term. At this time, all Fts3 queries must contain at least |
- one term or phrase that is not preceded by the '-' prefix. |
- |
- Regardless of whether or not a table name or column name is used on the |
- left hand side of the MATCH operator, a specific column of the fts3 table |
- may be associated with each token in a query by preceding a token with |
- a column name followed by a ':' character. For example, regardless of what |
- is specified for <col>, the following query requires that column "col1" |
- of the table contains the term "hello", and that column "col2" of the |
- table contains the term "world". If the table does not contain columns |
- named "col1" and "col2", then an error is returned and the query is |
- not run. |
- |
- <col> MATCH 'col1:hello col2:world' |
- |
- It is not possible to associate a specific table column with a quoted |
- phrase or a term preceded by a '-' operator. A '*' character may be |
- appended to a term associated with a specific column for prefix matching. |
- |
-3. ENHANCED QUERY SYNTAX |
- |
- The enhanced query syntax is quite similar to the standard query syntax, |
- with the following four differences: |
- |
- 1) Parenthesis are supported. When using the enhanced query syntax, |
- parenthesis may be used to overcome the built-in precedence of the |
- supplied binary operators. For example, the following query: |
- |
- <col> MATCH '(hello world) OR (simple example)' |
- |
- matches documents that contain both "hello" and "world", and documents |
- that contain both "simple" and "example". It is not possible to forumlate |
- such a query using the standard syntax. |
- |
- 2) Instead of separating tokens and phrases by whitespace, an AND operator |
- may be explicitly specified. This does not change query processing at |
- all, but may be used to improve readability. For example, the following |
- query is handled identically to the one above: |
- |
- <col> MATCH '(hello AND world) OR (simple AND example)' |
- |
- As with the OR and NEAR operators, the AND operator must be specified |
- in upper case. The word "and" specified in lower or mixed case is |
- handled as a regular token. |
- |
- 3) The '-' token prefix is not supported. Instead, a new binary operator, |
- NOT, is included. The NOT operator requires that the query specified |
- as its left-hand operator matches, but that the query specified as the |
- right-hand operator does not. For example, to query for all rows that |
- contain the term "example" but not the term "simple", the following |
- query could be used: |
- |
- <col> MATCH 'example NOT simple' |
- |
- As for all other operators, the NOT operator must be specified in |
- upper case. Otherwise it will be treated as a regular token. |
- |
- 4) Unlike in the standard syntax, where the OR operator has a higher |
- precedence than the implicit AND operator, when using the enhanced |
- syntax implicit and explict AND operators have a higher precedence |
- than OR operators. Using the enhanced syntax, the following two |
- queries are equivalent: |
- |
- <col> MATCH 'sqlite fantastic OR impressive' |
- <col> MATCH '(sqlite AND fantastic) OR impressive' |
- |
- however, when using the standard syntax, the query: |
- |
- <col> MATCH 'sqlite fantastic OR impressive' |
- |
- is equivalent to the enhanced syntax query: |
- |
- <col> MATCH 'sqlite AND (fantastic OR impressive)' |
- |
- The precedence of all enhanced syntax operators, in order from highest |
- to lowest, is: |
- |
- NEAR (highest precedence, tightest grouping) |
- NOT |
- AND |
- OR (lowest precedence, loosest grouping) |
- |
- Using the advanced syntax, it is possible to specify expressions enclosed |
- in parenthesis as operands to the NOT, AND and OR operators. However both |
- the left and right hand side operands of NEAR operators must be either |
- tokens or phrases. Attempting the following query will return an error: |
- |
- <col> MATCH 'sqlite NEAR (fantastic OR impressive)' |
- |
- Queries of this form must be re-written as: |
- |
- <col> MATCH 'sqlite NEAR fantastic OR sqlite NEAR impressive' |