OLD | NEW |
(Empty) | |
| 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' |
OLD | NEW |