摘要:
select row_number() over(order by a) AS row_id,b,c from T 阅读全文
摘要:
今天创建视图的时候,sql语句为 select * from (select a from A union select b from B ) as C,但是查询1000条数据,居然花了45s的时间,于是查询了资料,资料显示: UNION 因为会将各查询子集的记录做比较,故比起UNION ALL , 阅读全文