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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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
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13 SQL Statement Syntax
13.2 Data Manipulation Statements
13.2.4 HANDLER SyntaxHANDLER 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 CLOSEmysql> 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语句注意事项
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原文链接：http://blog.itpub.net/9240380/viewspace-2666381/
