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|Comment:||Add the file ext/fts3/README.syntax, containing documentation describing the two query syntaxes now supported by fts3. (CVS 6042)|
|Downloads:||Tarball | ZIP archive | SQL archive|
|Timelines:||family | ancestors | descendants | both | trunk|
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|User & Date:||danielk1977 2008-12-19 11:37:39|
|16:31||Add some crash-tests for savepoint. Fix a bug revealed by these tests. (CVS 6043) check-in: 6f36c166 user: danielk1977 tags: trunk|
|11:37||Add the file ext/fts3/README.syntax, containing documentation describing the two query syntaxes now supported by fts3. (CVS 6042) check-in: ed81ad5a user: danielk1977 tags: trunk|
|22:25||Fix the Oracle and MS-Sql command-line terminator logic in the CLI. Ticket #3544. (CVS 6041) check-in: dcc8935f user: drh tags: trunk|
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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_FTS3_ENABLE_PARENTHESIS defined. -DSQLITE_FTS3_ENABLE_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'