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handler類似于select語(yǔ)句,但又不同于后者,它只能每次查詢1次記錄。handler有一些特殊的功能,適用于一些特定的場(chǎng)景。本文介紹handler語(yǔ)句相關(guān)的一些知識(shí),以便后用。
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handler語(yǔ)句官方手冊(cè)
handler語(yǔ)句語(yǔ)法
handler語(yǔ)句示例
handler語(yǔ)句適用場(chǎng)景
handler語(yǔ)句注意事項(xiàng)
13 SQL Statement Syntax 13.2 Data Manipulation Statements 13.2.4 HANDLER Syntax
HANDLER tbl_name OPEN [ [AS] alias] HANDLER tbl_name READ index_name { = | <= | >= | < | > } (value1,value2,...) [ WHERE where_condition ] [LIMIT ... ] HANDLER tbl_name READ index_name { FIRST | NEXT | PREV | LAST } [ WHERE where_condition ] [LIMIT ... ] HANDLER tbl_name READ { FIRST | NEXT } [ WHERE where_condition ] [LIMIT ... ] HANDLER tbl_name CLOSE
為handle指定一個(gè)別名用于使用多個(gè)handle
HANDLER tbl_name OPEN [ [AS] alias]
mysql> handler t_table_lock open p1; Query OK, 0 rows affected (0.00 sec)
打開表和關(guān)閉表
HANDLER tbl_name OPEN [ [AS] alias] HANDLER tbl_name CLOSE
mysql> handler t_table_lock open; Query OK, 0 rows affected (0.00 sec) mysql> show open tables from zxydb like 't_table_lock'; +----------+--------------+--------+-------------+ | Database | Table | In_use | Name_locked | +----------+--------------+--------+-------------+ | zxydb | t_table_lock | 1 | 0 | +----------+--------------+--------+-------------+ 1 row in set (0.00 sec) mysql> handler t_table_lock close; Query OK, 0 rows affected (0.00 sec) ## mysql> show open tables from zxydb like 't_table_lock'; +----------+--------------+--------+-------------+ | Database | Table | In_use | Name_locked | +----------+--------------+--------+-------------+ | zxydb | t_table_lock | 0 | 0 | +----------+--------------+--------+-------------+ 1 row in set (0.00 sec)
讀取表的記錄
HANDLER tbl_name READ { FIRST | NEXT } [ WHERE where_condition ] [LIMIT ... ]
##獲取表第1條記錄 mysql> handler t_table_lock read first; +------+------+ | a | b | +------+------+ | 1 | 1 | +------+------+ 1 row in set (0.00 sec) ##獲取表的下一條記錄 mysql> handler t_table_lock read next; Empty set (0.00 sec)
獲取指定索引值的表記錄
HANDLER tbl_name READ index_name { = | <= | >= | < | > } (value1,value2,...) [ WHERE where_condition ] [LIMIT ... ]
mysql> handler t_table_lock read idx_a=(1); +------+------+ | a | b | +------+------+ | 1 | 1 | +------+------+ 1 row in set (0.00 sec) ## mysql> handler t_table_lock read idx_a=(2); Empty set (0.00 sec)
獲取指定索引的第一,下一,前一,最后的表記錄
HANDLER tbl_name READ index_name { FIRST | NEXT | PREV | LAST } [ WHERE where_condition ] [LIMIT ... ]
## mysql> handler t_table_lock read idx_a first; +------+------+ | a | b | +------+------+ | 1 | 1 | +------+------+ 1 row in set (0.00 sec) ## mysql> handler t_table_lock read idx_a next; Empty set (0.00 sec) ## mysql> handler t_table_lock read idx_a last; +------+------+ | a | b | +------+------+ | 1 | 1 | +------+------+ 1 row in set (0.00 sec) ## mysql> handler t_table_lock read idx_a prev; Empty set (0.00 sec)
handler語(yǔ)句注意事項(xiàng)
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