摘要:
比如: select id, name from table1 where name = 'x' union all select id, name from table2 where name = 'x' 与select * from (select id, name from table1 阅读全文
摘要:
EXITS 和 IN 的区别: 从效率来看: 1) select * from T1 where exists(select 1 from T2 where T1.a=T2.a) ; T1数据量小而T2数据量非常大时,T1<<T2 时,1) 的查询效率高。 2) select * from T1 w 阅读全文