# groonga - An open-source fulltext search engine and column store.

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# 8.10.1. Query syntax

Query syntax is a syntax to specify search condition for common Web search form. It is similar to the syntax of Google's search form. For example, `word1 word2` means that groonga searches records that contain both `word1` and `word2`. `word1 OR word2` means that groogna searches records that contain either `word1` or `word2`.

Query syntax consists of `conditional expression`, `combind expression` and `assignment expression`. Nomrally `assignment expression` can be ignored. Because `assignment expression` is disabled in `--query` option of select. You can use it if you use groonga as library and customize query syntax parser options.

`Conditinal expression` specifies an condition. `Combinded expression` consists of one or more `conditional expression`, `combined expression` or `assignment expression`. `Assignment expression` can assigns a column to a value.

## 8.10.1.1. Sample data

Here are a schema definition and sample data to show usage.

Execution example:

    table_create Entries TABLE_PAT_KEY ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Entries content COLUMN_SCALAR Text
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Entries n_likes COLUMN_SCALAR UInt32
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create Terms TABLE_PAT_KEY|KEY_NORMALIZE ShortText --default_tokenizer TokenBigram
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Terms entries_key_index COLUMN_INDEX|WITH_POSITION Entries _key
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Terms entries_content_index COLUMN_INDEX|WITH_POSITION Entries content
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    load --table Entries
    [
    {"_key":    "The first post!",
     "content": "Welcome! This is my first post!",
     "n_likes": 5},
    {"_key":    "Groonga",
     "content": "I started to use groonga. It's very fast!",
     "n_likes": 10},
    {"_key":    "Mroonga",
     "content": "I also started to use mroonga. It's also very fast! Really fast!",
     "n_likes": 15},
    {"_key":    "Good-bye Senna",
     "content": "I migrated all Senna system!",
     "n_likes": 3},
    {"_key":    "Good-bye Tritonn",
     "content": "I also migrated all Tritonn system!",
     "n_likes": 3}
    ]
    # [[0, 1337566253.89858, 0.000355720520019531], 5]

There is a table, `Entries`, for blog entries. An entry has title, content and the number of likes for the entry. Title is key of `Entries`. Content is value of `Entries.content` column. The number of likes is value of `Entries.n_likes` column.

`Entries._key` column and `Entries.content` column are indexed using `TokenBigram` tokenizer. So both `Entries._key` and `Entries.content` are fulltext search ready.

OK. The schema and data for examples are ready.

## 8.10.1.2. Escape

There are special characters in query syntax. To use a special character as itself, it should be escaped by prepending `\`. For example, `"` is a special character. It is escaped as `\"`.

Here is a special character list:

> - `[space]` (escaped as `[backslash][space]`) (You should substitute `[space]` with a white space character that is 0x20 in ASCII and `[backslash]` with `\\`.)
> - `"` (escaped as `\"`)
> - `'` (escaped as `\'`)
> - `(` (escaped as `\(`)
> - `)` (escaped as `\)`)
> - `\` (escaped as `\\`)

You can use quote instead of escape. Quote syntax is `"..."` or `'...'`. You need escape `"` as `\"` in `"..."` quote syntax. You need escape `'` as `\'` in `'...'` quote syntax. For example, `Alice's brother (Bob)` can be quoted `"Alice's brother (Bob)"` or `'Alice\'s brother (Bob)'`.

Note

There is a important point which you have to care. The ''\'' (backslash) character is interpreted by command line shell. So if you want to search ''('' itself for example, you need to escape twice (''\\('') in command line shell. The command line shell interprets ''\\('' as ''\('', then pass such a literal to groonga. groonga regards ''\('' as ''('', then search ''('' itself from database. If you can't do intended search by groonga, confirm whether special character is escaped properly.

## 8.10.1.3. Conditional expression

Here is available conditional expression list.

### 8.10.1.3.1. Full text search condition

Its syntax is `keyword`.

`Full text search condition` specifies a full text search condition against the default match columns. Match columns are full text search target columns.

You should specify the default match columns for full text search. They can be specified by `--match_columns` option of select. If you don't specify the default match columns, this conditional expression fails.

This conditional expression does full text search with `keyword`. `keyword` should not contain any spaces. If `keyword` contains a space such as `search keyword`, it means two full text search conditions; `search` and `keyword`. If you want to specifies a keyword that contains one or more spaces, you can use `phrase search condition` that is described below.

Here is a simple exmaple.

Execution example:

    select Entries --match_columns content --query fast
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that contain a word `fast` in `content` column value.

`content` column is the default match column.

### 8.10.1.3.2. Phrase search condition

Its syntax is `"search keyword"`.

`Phrase search condition` specifies a phrase search condition against the default match columns.

You should specify the default match columns for full text search. They can be specified by `--match_columns` option of select. If you don't specify the default match columns, this conditional expression fails.

This conditional expression does phrase search with `search keyword`. Phrase search searches records that contain `search` and `keyword` and those terms are appeared in the same order and adjacent. Thus, `Put a search keyword in the form` is matched but `Search by the keyword` and `There is a keyword. Search by it!` aren't matched.

Here is a simple exmaple.

Execution example:

    select Entries --match_columns content --query '"I started"'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that contain a phrase `I started` in `content` column value. `I also started` isn't matched because `I` and `started` aren't adjacent.

`content` column is the default match column.

### 8.10.1.3.3. Full text search condition (with explicit match column)

Its syntax is `column:@keyword`.

It's similar to `full text search condition` but it doesn't require the default match columns. You need to specify match column for the full text search condition by `column:` instead of `--match_columns` option of select.

This condtional expression is useful when you want to use two or more full text search against different columns. The default match columns specified by `--match_columns` option can't be specified multiple times. You need to specify the second match column by this conditional expression.

The different between `full text search condition` and `full text search condition (with explicit match column)` is whether advanced match columns are supported or not. `Full text search condition` supports advanced match columns but `full text search condition (with explicit match column)` isn't supported. Advanced match columns has the following features:

> - Weight is supported.
> - Using multiple columns are supported.
> - Using index column as a match column is supported.

See description of `--match_columns` option of select about them.

Here is a simple exmaple.

Execution example:

    select Entries --query content:@fast
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that contain a word `fast` in `content` column value.

### 8.10.1.3.4. Phrase search condition (with explicit match column)

Its syntax is `column:@"search keyword"`.

It's similar to `phrase search condition` but it doesn't require the default match columns. You need to specify match column for the phrase search condition by `column:` instead of `--match_columns` option of select.

The different between `phrase search condition` and `phrase search condition (with explicit match column)` is similar to between `full text search condition` and `full text search condition (with explicit match column)`. `Phrase search condition` supports advanced match columns but `phrase search condition (with explicit match column)` isn't supported. See description of `full text search condition (with explicit match column)` about advanced match columns.

Here is a simple exmaple.

Execution example:

    select Entries --query 'content:@"I started"'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that contain a phrase `I started` in `content` column value. `I also started` isn't matched because `I` and `started` aren't adjacent.

### 8.10.1.3.5. Prefix search condition

Its syntax is `column:^value` or `value*`.

This conditional expression does prefix search with `value`. Prefix search searches records that contain a word that starts with `value`.

You can use fast prefix search against a column. The column must be indexed and index table must be patricia trie table (`TABLE_PAT_KEY`) or double array trie table (`TABLE_DAT_KEY`). You can also use fast prefix search against `_key` pseudo column of patricia trie table or double array trie table. You don't need to index `_key`.

Prefix search can be used with other table types but it causes all records scan. It's not problem for small records but it spends more time for large records.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query '_key:^Goo'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         5,
    #         "Good-bye Tritonn",
    #         "I also migrated all Tritonn system!",
    #         3
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that contain a word that starts with `Goo` in `_key` pseudo column value. `Good-bye Senna` and `Good-bye Tritonn` are matched with the expression.

### 8.10.1.3.6. Suffix search condition

Its syntax is `column:$value`.

This conditional expression does suffix search with `value`. Suffix search searches records that contain a word that ends with `value`.

You can use fast suffix search against a column. The column must be indexed and index table must be patricia trie table (`TABLE_PAT_KEY`) with `KEY_WITH_SIS` flag. You can also use fast suffix search against `_key` pseudo column of patricia trie table (`TABLE_PAT_KEY`) with `KEY_WITH_SIS` flag. You don't need to index `_key`. We recommended that you use index column based fast suffix search instead of `_key` based fast suffix search. `_key` based fast suffix search returns automatically registered substrings. (TODO: write document about suffix search and link to it from here.)

Note

Fast suffix search can be used only for non-ASCII characters such as hiragana in Japanese. You cannot use fast suffix search for ASCII character.

Suffix search can be used with other table types or patricia trie table without `KEY_WITH_SIS` flag but it causes all records scan. It's not problem for small records but it spends more time for large records.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple. It uses fast suffix search for hiragana in Japanese that is one of non-ASCII characters.

Execution example:

    table_create Titles TABLE_NO_KEY
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create Titles content COLUMN_SCALAR ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    table_create SuffixSearchTerms TABLE_PAT_KEY|KEY_WITH_SIS ShortText
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    column_create SuffixSearchTerms index COLUMN_INDEX Titles content
    # [[0, 1337566253.89858, 0.000355720520019531], true]
    load --table Titles
    [
    {"content": "ぐるんが"},
    {"content": "むるんが"},
    {"content": "せな"},
    {"content": "とりとん"}
    ]
    # [[0, 1337566253.89858, 0.000355720520019531], 4]
    select Titles --query 'content:$んが'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "content",
    #           "ShortText"
    #         ]
    #       ],
    #       [
    #         2,
    #         "むるんが"
    #       ],
    #       [
    #         1,
    #         "ぐるんが"
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that have value that ends with `んが` in `content` column value. `ぐるんが` and `むるんが` are matched with the expression.

### 8.10.1.3.7. Equal condition

Its syntax is `column:value`.

It matches records that `column` value is equal to `value`.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query _key:Groonga
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `_key` column value is equal to `Groonga`.

### 8.10.1.3.8. Not equal condition

Its syntax is `column:!value`.

It matches records that `column` value isn't equal to `value`.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query _key:!Groonga
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         4
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ],
    #       [
    #         5,
    #         "Good-bye Tritonn",
    #         "I also migrated all Tritonn system!",
    #         3
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ],
    #       [
    #         1,
    #         "The first post!",
    #         "Welcome! This is my first post!",
    #         5
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `_key` column value is not equal to `Groonga`.

### 8.10.1.3.9. Less than condition

Its syntax is `column:<value`.

It matches records that `column` value is less than `value`.

If `column` type is numerical type such as `Int32`, `column` value and `value` are compared as number. If `column` type is text type such as `ShortText`, `column` value and `value` are compared as bit sequence.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query n_likes:<10
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         3
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ],
    #       [
    #         5,
    #         "Good-bye Tritonn",
    #         "I also migrated all Tritonn system!",
    #         3
    #       ],
    #       [
    #         1,
    #         "The first post!",
    #         "Welcome! This is my first post!",
    #         5
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is less than `10`.

### 8.10.1.3.10. Greater than condition

Its syntax is `column:>value`.

It matches records that `column` value is greater than `value`.

If `column` type is numerical type such as `Int32`, `column` value and `value` are compared as number. If `column` type is text type such as `ShortText`, `column` value and `value` are compared as bit sequence.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query n_likes:>10
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is greater than `10`.

### 8.10.1.3.11. Less than or equal to condition

Its syntax is `column:<=value`.

It matches records that `column` value is less than or equal to `value`.

If `column` type is numerical type such as `Int32`, `column` value and `value` are compared as number. If `column` type is text type such as `ShortText`, `column` value and `value` are compared as bit sequence.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query n_likes:<=10
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         4
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ],
    #       [
    #         5,
    #         "Good-bye Tritonn",
    #         "I also migrated all Tritonn system!",
    #         3
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ],
    #       [
    #         1,
    #         "The first post!",
    #         "Welcome! This is my first post!",
    #         5
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is less than or equal to `10`.

### 8.10.1.3.12. Greater than or equal to condition

Its syntax is `column:>=value`.

It matches records that `column` value is greater than or equal to `value`.

If `column` type is numerical type such as `Int32`, `column` value and `value` are compared as number. If `column` type is text type such as `ShortText`, `column` value and `value` are compared as bit sequence.

It doesn't require the default match columns such as `full text search condition` and `phrase search condition`.

Here is a simple exmaple.

Execution example:

    select Entries --query n_likes:>=10
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is greater than or equal to `10`.

## 8.10.1.4. Combined expression

Here is available combined expression list.

### 8.10.1.4.1. Logical OR

Its syntax is `a OR b`.

`a` and `b` are conditional expressions, conbinded expressions or assignment expressions.

If at least one of `a` and `b` are matched, `a OR b` is matched.

Here is a simple exmaple.

Execution example:

    select Entries --query 'n_likes:>10 OR content:@senna'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         2
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is greater than `10` or contain a word `senna` in `content` column value.

### 8.10.1.4.2. Logical AND

Its syntax is `a + b` or just `a b`.

`a` and `b` are conditional expressions, conbinded expressions or assignment expressions.

If both `a` and `b` are matched, `a + b` is matched.

You can specify `+` the first expression such as `+a`. The `+` is just ignored.

Here is a simple exmaple.

Execution example:

    select Entries --query 'n_likes:>=10 + content:@groonga'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is greater than or equal to `10` and contain a word `groonga` in `content` column value.

### 8.10.1.4.3. Logical NOT

Its syntax is `a - b`.

`a` and `b` are conditional expressions, conbinded expressions or assignment expressions.

If `a` is matched and `b` is not matched, `a - b` is matched.

You can not specify `-` the first expression such as `-a`. It's syntax error.

Here is a simple exmaple.

Execution example:

    select Entries --query 'n_likes:>=10 - content:@groonga'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]

The expression matches records that `n_likes` column value is greater than or equal to `10` and don't contain a word `groonga` in `content` column value.

### 8.10.1.4.4. Grouping

Its syntax is `(...)`. `...` is space separated expression list.

`(...)` groups one ore more expressions and they can be processed as an expression. `a b OR c` means that `a` and `b` are matched or `c` is matched. `a (b OR c)` means that `a` and one of `b` and `c` are matched.

Here is a simple exmaple.

Execution example:

    select Entries --query 'n_likes:<5 content:@senna OR content:@fast'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         3
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ],
    #       [
    #         2,
    #         "Groonga",
    #         "I started to use groonga. It's very fast!",
    #         10
    #       ],
    #       [
    #         3,
    #         "Mroonga",
    #         "I also started to use mroonga. It's also very fast! Really fast!",
    #         15
    #       ]
    #     ]
    #   ]
    # ]
    select Entries --query 'n_likes:<5 (content:@senna OR content:@fast)'
    # [
    #   [
    #     0,
    #     1337566253.89858,
    #     0.000355720520019531
    #   ],
    #   [
    #     [
    #       [
    #         1
    #       ],
    #       [
    #         [
    #           "_id",
    #           "UInt32"
    #         ],
    #         [
    #           "_key",
    #           "ShortText"
    #         ],
    #         [
    #           "content",
    #           "Text"
    #         ],
    #         [
    #           "n_likes",
    #           "UInt32"
    #         ]
    #       ],
    #       [
    #         4,
    #         "Good-bye Senna",
    #         "I migrated all Senna system!",
    #         3
    #       ]
    #     ]
    #   ]
    # ]

The first expression doesn't use grouping. It matches records that `n_likes:<5` and `content:@senna` are matched or `content:@fast` is matched.

The second expression uses grouping. It matches records that `n_likes:<5` and one of `content:@senna` or `content:@fast` are matched.

## 8.10.1.5. Assignment expression

This section is for advanced users. Because assignment expression is disabled in `--query` option of select by default. You need to specify `ALLOW_COLUMN|ALLOW_UPDATE` as `--query_flags` option value to enable assignment expression.

Assignment expression in query syntax has some limitations. So you should use Script syntax instead of query syntax for assignment.

There is only one syntax for assignment expression. It's `column:=value`.

`value` is assigend to `column`. `value` is always processed as string in query syntax. `value` is casted to the type of `column` automatically. It causes some limitations. For example, you cannot use boolean literal such as `true` and `false` for `Bool` type column. You need to use empty string for `false` but query syntax doesn't support `column:=` syntax.

See Cast about cast.

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