select * from t_table_1 where task_id in (select id from t_table_2 where uid = #{uid}) 回到这条简单sql,包含子查询,按照我们的理解,mysql应该是先执行子查询:select id from t_table_2 where uid = #{uid},然后再执行外部查询:select * from t_table_1 where task_id in(),但这不一定,...
C# LINQ one condition, return multiple columns and rows C# LINQ order by not working for a SQL table with a primary key C# LinQ query to pull top 3 records from data table C# List vs IList C# List<>: How to read the data? C# List<struct> vs List<class> memory usage C# LITHUANIAN...
Multiple-TableSyntaxDELETE[LOW_PRIORITY][QUICK][IGNORE]tbl_name[.*][, tbl_name[.*]] ...FROMtable_references[WHERE where_condition]DELETE[LOW_PRIORITY][QUICK][IGNORE]FROMtbl_name[.*][, tbl_name[.*]] ... USING table_references[WHERE where_condition]PrivilegesYou need theDELETEprivilegeonata...
Summary: in this tutorial, you will learn how to use MySQL ON DELETE CASCADE referential action for a foreign key to delete data from multiple related tables. In the previous tutorial, you learned how to delete data from multiple related tables using a single DELETE statement. However, MySQL ...
开始我们拿sql到数据库查询平台查库执行计划,无奈这个平台有bug,delete语句无法查看,所以我们改成select,“应该”是一样。这个“应该”加了双引号,导致我们走了一点弯路。 EXPLAINSELECT*fromt_table_1wheretask_idin(selectidfromt_table_2whereuid=1)
DELETEFROMemployees;Code language:SQL (Structured Query Language)(sql) 3) Deleting related rows from multiple tables It becomes more complicated when you want to delete a row in a table that is associated with other rows in another table. ...
I was trying to run a DELETE query on multiple tables and I kept getting this error: The DELETE statement conflicted with the REFERENCE constraint I’m not that great with SQL, but I can get by. DELETEs have always been somethng that have given me trouble. So, I thought I’d share ...
652 rows deleted.Code language:SQL (Structured Query Language)(sql) D) Oracle DELETE – delete cascade In practice, you often delete a row from a table that has a foreign key relationship with rows from other tables. For example, you want to delete the sales order with id 1 from theorde...
We can join multiple tables in the DELETE statement, just like in the SELECT statement. DELETE data from a table by joining with another table in SQL Let us consider the below tables. CREATETABLEorders(order_idINTPRIMARYKEY,customer_nameVARCHAR(100),order_dateDATETIME,total_ordersINT);INSERT...
EXPLAIN SELECT * FROM yp_user IGNORE INDEX(idx_gender) where gender=1 ; 在我看来,虽然有MySQL Hints这种好用的工具,但我建议还是不要再生产环境使用,因为当数据量增长时,你压根儿都不知道这种索引的方式是否还适应于当前的环境,还是得配合DBA从索引的结构上去优化。