You can see that the SET clause includes a subquery, which finds the MAX value of the price column in the product table and multiplies it by 1.2 to add 20%. Finally, the WHERE clause is outside the subquery to only update the product_id of 1, as it applies to UPDATE rather than to...
2 DEPENDENT SUBQUERY b (NULL) eq_ref PRIMARY,idx_user_name PRIMARY 98 settlement_data.a.pay_id 1 5.00 Using where 从执行计划可以看出该 update 子查询,优化器先执行了 id 为2的 (DEPENDENT SUBQUERY )相关子查询部分,然后通过对 PRIMARY 以索引全扫描方式对全表 155041 行数据加锁主锁,来执行的 updat...
MySQL中的子查询(Subquery)是指嵌套在另一个查询中的查询。子查询可以出现在SELECT、FROM、WHERE、HAVING和UPDATE语句中。当子查询用在UPDATE语句中时,它允许你基于另一个表或同一表中的数据来更新记录。 相关优势 灵活性:子查询提供了在单个SQL语句中执行多个操作的能力。
1、在优化DELETE/UPDATE语句时,通常会将DELETE/UPDATE语句改写成SELECT语句进行测试,以避免测试操作导致数据变更,需要注意两者的执行计划可能不同。 2、当IN语句生产的执行计划为DEPENDENT SUBQUERY类型时,需要考虑外表的循环数量,如果外表循环次数较大,可以考虑调整SQL语句(如关联查询)来优化内外表位置。
(NULL) 155182 100.00 Using where 2 DEPENDENT SUBQUERY b (NULL) unique_subquery PRIMARY,IDX_PAY_MAIN_PAY_TIME PRIMARY 98 func 1 46.46 Using where DELETE a FROM pay_stream a WHERE a.pay_id NOT IN (SELECT b.pay_id FROM pay_main b WHERE b.pay_time >= '2017-08-12 00:00:00'); ...
SUBQUERY: 在SELECT或者WHERE列表中包含了子查询,该子查询被标记为SUBQUERY. DERIVED: 在FROM列表中包含的子查询被标记为DERIVED. UNION: 若第二个SELECT出现在UNION之后,则被标记为UNION;若UNION包含在FROM子句的子查询中,则被标记为DERIVED. UNION RESULT 从UNION表获取结果的SELECT被标记为UNION RESULT. ...
Works with: SQL Server, PostgreSQL (not Oracle, MySQL) You can use a subquery in theWITH clause(called a CTE or Common Table Expression) to update data in one table from another table. WITHsubqueryAS(SELECTaccount_id,account_number,person_idFROMaccount)UPDATEpersonSETaccount_number=subquery.acco...
错误提示是:ERROR 1093 (HY000): You can't specify target table 'apples' for update in FROM clause. MySQL手册UPDATE documentation这下面有说明 : “Currently, you cannot update a table and select from the same table in a subquery.” 在这个例子中,要解决问题也十分简单,但有时候不得不通过查询子句...
When you use a correlated subquery in an UPDATE statement, the correlation name refers to the rows that you want to update. For example, when all activities of a project must be completed before September 1983, your department considers that project to be a priority project. You can use the...
Here, the SQL query updates thefirst_nametoAlicein theCustomerstable for those who ordered aMonitorand whose shipping status isDelivered. UPDATE With Subquery Using a subquery within theWHEREclause can mimic theJOINbehavior in SQLite. For example, ...