查询表中 A/B 字段联合是否唯一
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SELECT column_a,column_b,COUNT(*) as num FROM TABLE GROUP BY column_a,column_b; SELECT column_a,column_b,COUNT(*) as num FROM TABLE group by column_a,column_b having count(*)>1;
SELECT column_a,column_b,COUNT(*) as num FROM TABLE GROUP BY column_a,column_b;
SELECT column_a,column_b,COUNT(*) as num FROM TABLE group by column_a,column_b having count(*)>1;