Annotation of embedaddon/sqlite3/ext/fts3/README.syntax, revision 1.1.1.1
1.1 misho 1:
2: 1. OVERVIEW
3:
4: This README file describes the syntax of the arguments that may be passed to
5: the FTS3 MATCH operator used for full-text queries. For example, if table
6: "t1" is an Fts3 virtual table, the following SQL query:
7:
8: SELECT * FROM t1 WHERE <col> MATCH <full-text query>
9:
10: may be used to retrieve all rows that match a specified for full-text query.
11: The text "<col>" should be replaced by either the name of the fts3 table
12: (in this case "t1"), or by the name of one of the columns of the fts3
13: table. <full-text-query> should be replaced by an SQL expression that
14: computes to a string containing an Fts3 query.
15:
16: If the left-hand-side of the MATCH operator is set to the name of the
17: fts3 table, then by default the query may be matched against any column
18: of the table. If it is set to a column name, then by default the query
19: may only match the specified column. In both cases this may be overriden
20: as part of the query text (see sections 2 and 3 below).
21:
22: As of SQLite version 3.6.8, Fts3 supports two slightly different query
23: formats; the standard syntax, which is used by default, and the enhanced
24: query syntax which can be selected by compiling with the pre-processor
25: symbol SQLITE_ENABLE_FTS3_PARENTHESIS defined.
26:
27: -DSQLITE_ENABLE_FTS3_PARENTHESIS
28:
29: 2. STANDARD QUERY SYNTAX
30:
31: When using the standard Fts3 query syntax, a query usually consists of a
32: list of terms (words) separated by white-space characters. To match a
33: query, a row (or column) of an Fts3 table must contain each of the specified
34: terms. For example, the following query:
35:
36: <col> MATCH 'hello world'
37:
38: matches rows (or columns, if <col> is the name of a column name) that
39: contain at least one instance of the token "hello", and at least one
40: instance of the token "world". Tokens may be grouped into phrases using
41: quotation marks. In this case, a matching row or column must contain each
42: of the tokens in the phrase in the order specified, with no intervening
43: tokens. For example, the query:
44:
45: <col> MATCH '"hello world" joe"
46:
47: matches the first of the following two documents, but not the second or
48: third:
49:
50: "'Hello world', said Joe."
51: "One should always greet the world with a cheery hello, thought Joe."
52: "How many hello world programs could their be?"
53:
54: As well as grouping tokens together by phrase, the binary NEAR operator
55: may be used to search for rows that contain two or more specified tokens
56: or phrases within a specified proximity of each other. The NEAR operator
57: must always be specified in upper case. The word "near" in lower or mixed
58: case is treated as an ordinary token. For example, the following query:
59:
60: <col> MATCH 'engineering NEAR consultancy'
61:
62: matches rows that contain both the "engineering" and "consultancy" tokens
63: in the same column with not more than 10 other words between them. It does
64: not matter which of the two terms occurs first in the document, only that
65: they be seperated by only 10 tokens or less. The user may also specify
66: a different required proximity by adding "/N" immediately after the NEAR
67: operator, where N is an integer. For example:
68:
69: <col> MATCH 'engineering NEAR/5 consultancy'
70:
71: searches for a row containing an instance of each specified token seperated
72: by not more than 5 other tokens. More than one NEAR operator can be used
73: in as sequence. For example this query:
74:
75: <col> MATCH 'reliable NEAR/2 engineering NEAR/5 consultancy'
76:
77: searches for a row that contains an instance of the token "reliable"
78: seperated by not more than two tokens from an instance of "engineering",
79: which is in turn separated by not more than 5 other tokens from an
80: instance of the term "consultancy". Phrases enclosed in quotes may
81: also be used as arguments to the NEAR operator.
82:
83: Similar to the NEAR operator, one or more tokens or phrases may be
84: separated by OR operators. In this case, only one of the specified tokens
85: or phrases must appear in the document. For example, the query:
86:
87: <col> MATCH 'hello OR world'
88:
89: matches rows that contain either the term "hello", or the term "world",
90: or both. Note that unlike in many programming languages, the OR operator
91: has a higher precedence than the AND operators implied between white-space
92: separated tokens. The following query matches documents that contain the
93: term 'sqlite' and at least one of the terms 'fantastic' or 'impressive',
94: not those that contain both 'sqlite' and 'fantastic' or 'impressive':
95:
96: <col> MATCH 'sqlite fantastic OR impressive'
97:
98: Any token that is part of an Fts3 query expression, whether or not it is
99: part of a phrase enclosed in quotes, may have a '*' character appended to
100: it. In this case, the token matches all terms that begin with the characters
101: of the token, not just those that exactly match it. For example, the
102: following query:
103:
104: <col> MATCH 'sql*'
105:
106: matches all rows that contain the term "SQLite", as well as those that
107: contain "SQL".
108:
109: A token that is not part of a quoted phrase may be preceded by a '-'
110: character, which indicates that matching rows must not contain the
111: specified term. For example, the following:
112:
113: <col> MATCH '"database engine" -sqlite'
114:
115: matches rows that contain the phrase "database engine" but do not contain
116: the term "sqlite". If the '-' character occurs inside a quoted phrase,
117: it is ignored. It is possible to use both the '-' prefix and the '*' postfix
118: on a single term. At this time, all Fts3 queries must contain at least
119: one term or phrase that is not preceded by the '-' prefix.
120:
121: Regardless of whether or not a table name or column name is used on the
122: left hand side of the MATCH operator, a specific column of the fts3 table
123: may be associated with each token in a query by preceding a token with
124: a column name followed by a ':' character. For example, regardless of what
125: is specified for <col>, the following query requires that column "col1"
126: of the table contains the term "hello", and that column "col2" of the
127: table contains the term "world". If the table does not contain columns
128: named "col1" and "col2", then an error is returned and the query is
129: not run.
130:
131: <col> MATCH 'col1:hello col2:world'
132:
133: It is not possible to associate a specific table column with a quoted
134: phrase or a term preceded by a '-' operator. A '*' character may be
135: appended to a term associated with a specific column for prefix matching.
136:
137: 3. ENHANCED QUERY SYNTAX
138:
139: The enhanced query syntax is quite similar to the standard query syntax,
140: with the following four differences:
141:
142: 1) Parenthesis are supported. When using the enhanced query syntax,
143: parenthesis may be used to overcome the built-in precedence of the
144: supplied binary operators. For example, the following query:
145:
146: <col> MATCH '(hello world) OR (simple example)'
147:
148: matches documents that contain both "hello" and "world", and documents
149: that contain both "simple" and "example". It is not possible to forumlate
150: such a query using the standard syntax.
151:
152: 2) Instead of separating tokens and phrases by whitespace, an AND operator
153: may be explicitly specified. This does not change query processing at
154: all, but may be used to improve readability. For example, the following
155: query is handled identically to the one above:
156:
157: <col> MATCH '(hello AND world) OR (simple AND example)'
158:
159: As with the OR and NEAR operators, the AND operator must be specified
160: in upper case. The word "and" specified in lower or mixed case is
161: handled as a regular token.
162:
163: 3) The '-' token prefix is not supported. Instead, a new binary operator,
164: NOT, is included. The NOT operator requires that the query specified
165: as its left-hand operator matches, but that the query specified as the
166: right-hand operator does not. For example, to query for all rows that
167: contain the term "example" but not the term "simple", the following
168: query could be used:
169:
170: <col> MATCH 'example NOT simple'
171:
172: As for all other operators, the NOT operator must be specified in
173: upper case. Otherwise it will be treated as a regular token.
174:
175: 4) Unlike in the standard syntax, where the OR operator has a higher
176: precedence than the implicit AND operator, when using the enhanced
177: syntax implicit and explict AND operators have a higher precedence
178: than OR operators. Using the enhanced syntax, the following two
179: queries are equivalent:
180:
181: <col> MATCH 'sqlite fantastic OR impressive'
182: <col> MATCH '(sqlite AND fantastic) OR impressive'
183:
184: however, when using the standard syntax, the query:
185:
186: <col> MATCH 'sqlite fantastic OR impressive'
187:
188: is equivalent to the enhanced syntax query:
189:
190: <col> MATCH 'sqlite AND (fantastic OR impressive)'
191:
192: The precedence of all enhanced syntax operators, in order from highest
193: to lowest, is:
194:
195: NEAR (highest precedence, tightest grouping)
196: NOT
197: AND
198: OR (lowest precedence, loosest grouping)
199:
200: Using the advanced syntax, it is possible to specify expressions enclosed
201: in parenthesis as operands to the NOT, AND and OR operators. However both
202: the left and right hand side operands of NEAR operators must be either
203: tokens or phrases. Attempting the following query will return an error:
204:
205: <col> MATCH 'sqlite NEAR (fantastic OR impressive)'
206:
207: Queries of this form must be re-written as:
208:
209: <col> MATCH 'sqlite NEAR fantastic OR sqlite NEAR impressive'
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