sql查詢某字段的相同值:
SELECT * FROM table WHERE col in (SELECT col FROM table GROUP BY col HAVING COUNT (col) >1);
順帶說一下where和having：
select * from table
where ···(只能對(duì)分組前的屬性進(jìn)行篩選)
group by ···(按某個(gè)字段分組)
having ···(只能對(duì)分組后的每個(gè)組的整體屬性進(jìn)行篩選，用聚合函數(shù)體現(xiàn))
--不使用group by就默認(rèn)表的整體為一組
實(shí)例：
查詢出重復(fù)記錄
select * from 數(shù)據(jù)表 WHERE 重復(fù)記錄字段 in ( select 重復(fù)記錄字段 from 數(shù)據(jù)表 group by 重復(fù)記錄字段 having count(重復(fù)記錄字段)>1)
