mysql handler语句之一

handler语句概述

handler类似于select语句，但又不同于后者，它只能每次查询1次记录。handler有一些特殊的功能，适用于一些特定的场景。本文介绍handler语句相关的一些知识，以便后用。

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目录

• handler语句官方手册

• handler语句语法

• handler语句示例
  

• handler语句适用场景

• handler语句注意事项
  

handler语句官方手册

13 SQL Statement Syntax13.2 Data Manipulation Statements13.2.4 HANDLER Syntax

handler语句语法

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

handler语句示例

• 为handle指定一个别名用于使用多个handle

HANDLER tbl_name OPEN [ [AS] alias]

mysql> handler t_table_lock open p1;Query OK, 0 rows affected (0.00 sec)

• 打开表和关闭表

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)

• 读取表的记录

HANDLER tbl_name READ { FIRST | NEXT }    [ WHERE where_condition ] [LIMIT ... ]

##获取表第1条记录mysql> handler t_table_lock read first;+------+------+| a    | b    |+------+------+|    1 |    1 |+------+------+1 row in set (0.00 sec)##获取表的下一条记录mysql> handler t_table_lock read next;Empty set (0.00 sec)

• 获取指定索引值的表记录
  

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)

• 获取指定索引的第一，下一，前一，最后的表记录
  

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语句适用场景

handler语句注意事项