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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'
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