sql⾼效查询两表之间不同的数据
本⽂推荐三种⽅法，第三种为最⾼效
1.使⽤not in 结合 distinctselect distinct from
SELECT DISTINCT a.id FROM a WHERE a.id NOT in(SELECT id FROM b)
2.使⽤left join做关联查询且条件为关联表的id is null
SELECT * from a LEFT JOIN b ON a.id = b.id WHERE b.id IS NULL
3.充分利⽤count函数，若⼦查询的结果不为0，则表明该Id存在1条或多条，不会查询出此条记录，最⾼效！select * from b where (select count(1) from a where a.ID = b.ID) = 0