MySQL handler的用法与应用

handler的用法

HANDLER是一个比较低级的语句，具有自己的会话机制，且会话对象不由其他会话共享，且直到会话调用 HANDLER... CLOSE 或会话终止时才关闭

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 tbl_name OPEN [ [AS] alias]

1 2	handler tablename open; /开启tablename表 hand tablename open as new_tablename; /追加tablename的表的别名为new_tablename，此处不是修改，且只在当前会话内生效

HANDLER tbl_name READ index_name { = | <= | >= | < | > } (value1,value2,...)[ WHERE where_condition ] [LIMIT ... ]

1	handler tablename read Keyname=('test1'); /读取tablename表的索引名为Keyname的值为test1的整行信息(每张表都会默认有索引列）

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

1	handler tablename read listname first; /读取tablename表的列名为listname的第一个值的整行信息

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

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handler tablename read first;                  /读取tablename表的第一行信息。
handler tablename read next;                 /读取tablename表的下一行信息。
handler tablename read first limit 0,2;    /读取tablename表的前两行信息。

HANDLER tbl_name CLOSE

1	handler tablename close /退出handler会话（它于handler ... open是相对的）

例如：

已知一张表名为tablename，我们可以用下述语句

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handler tablename open;
handler tablename read frist;
handler tablename close;

或

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handler  tablename open as test;
handler test read frist;
handler test close;

应用-[强网杯 2019]随便注

本文采用署名-非商业性使用-相同方式共享 4.0 国际许可协议，转载请注明出处。