sql查询某字段的相同值:
SELECT * FROM table WHERE col in (SELECT col FROM table GROUP?BY col HAVING COUNT (col)?>1);
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顺带说一下where和having：
select * from table where ···(只能对分组前的属性进行筛选) group by ···(按某个字段分组) having ···(只能对分组后的每个组的整体属性进行筛选，用聚合函数体现) --不使用group by就默认表的整体为一组