mysql> UPDATE EACONTACTGROUPS A
SET GROUPNAME=(SELECT CONCAT(B.GROUPNAME,'-',A.GROUPNAME) FROM EACONTACTGROUPS B WHERE B.CORPID=A.CORPID AND B.USERID=A.USERID AND B.GROUPID=A.PARENTGROUPID)
WHERE A.PARENTGROUPID IS NOT NULL;
ERROR 1093 (HY000): You can't specify target table 'A' for update in FROM clause
上面是目前MYSQL5.0仍然有的限制Q文中_
In general, you cannot modify a table and select from the same table in a subquery. For example, this limitation applies to statements of the following forms:
DELETE FROM t WHERE ... (SELECT ... FROM t ...);UPDATE t ... WHERE col = (SELECT ... FROM t ...);{INSERT|REPLACE} INTO t (SELECT ... FROM t ...);
Exception: The preceding prohibition does not apply if you are using a subquery for the modified table in the
FROM
clause. Example:
UPDATE t ... WHERE col = (SELECT (SELECT ... FROM t...) AS _t ...);
Here the prohibition does not apply because a subquery in the
FROM
clause is materialized as a temporary table, so the relevant rows in
t
have already been selected by the time the update to
t
takes place. 依据文档Q改成下面的样子p了：
mysql> UPDATE EACONTACTGROUPS A
SET GROUPNAME=(SELECT CONCAT(B.GROUPNAME,'-',A.GROUPNAME) FROM ( SELECT GROUPNAME,CORPID,USERID,GROUPID,PARENTGROUPID FROM EACONTACTGROUPS) B
WHERE B.CORPID=A.CORPID AND B.USERID=A.USERID AND B.GROUPID=A.PARENTGROUPID)
WHERE A.PARENTGROUPID IS NOT NULL;
Query OK, 16 rows affected (0.01 sec)
Rows matched: 16 Changed: 16 Warnings: 0
?今天写一个删除语句时扑ֈ的一点资?解决了一个简单的删除语句.呵呵,以后注意?
原句:delete from menu_item where parent_id =(select menu_item_id from menu_item where menu_data like '%manageVendors%');
修改?delete from menu_item where parent_id =(select temp.menu_item_id from (select m.menu_item_id,m.menu_data from menu_item m) temp where temp.menu_data like '%manageVendors%');
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1、导出數據库為dbname的表l构Q其中用戶名為root,密码為dbpasswd,生成的脚本名為db.sqlQ?br /> mysqldump -uroot -pdbpasswd -d dbname >db.sql;
2、导出數據库為dbname某张?test)l构
mysqldump -uroot -pdbpasswd -d dbname test>db.sql;
3、导出數據库為dbname所有表l构及表數據Q不?dQ?br /> mysqldump -uroot -pdbpasswd dbname >db.sql;
4、导出數據库為dbname某张?test)l构及表數據Q不?dQ?br /> mysqldump -uroot -pdbpasswd dbname test>db.sql;
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很久沒用數據庫了Q媽的竟焉批量插表都忘記了。在這里记录一下?/p>
把表B中的字段Q插入到表A中；
INSERT INTO 表A(字段?, 字段?, ……) SELECT (字段?, 字段?, ……) FROM 表B;
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Q?QDELETE可以通过WHERE语句选择要删除的记录。但执行得速度不快Q可以返回被删除的记录数。而TRUNCATE TABLE无法删除指定的记录，而且不能q回被删除的记录。但它执行得非常快?br /> Q?Q分别执?/font>DELETE FROM Table_name?/font>TRUNCATE TABLE Table_name
Ҏ?/font>TRUNCATE TABLE Table_name后，Table_name?/font>自增水从新开始计，?/font>DELETE FROM Table_name则不会从新开始，会l之前的水受?/font>
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