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