如何根据一列中的值将唯一值选择到mysql表中？

Question

我有一个名为x的表

这是表x中的示例数据

Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3

一_ _ __ __ _ _ __ __ _ _ __ ___ b _ _ __ __ _ _ __ __ _ _ __ __ _ __ _c

a2_ _ __ _ __ __ _ _ _ __ __ _ _ _ B2 __ _ __ _ __ __ _ _ _ __ __ _ __ _c

a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2

a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3

我在新表中需要的结果是：

Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3

a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2

a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3

我尝试将值导入到新表中并在第3列上应用唯一索引，但我得到的结果是

Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3

a_ _ __ _ __ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c

a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2

a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3

Answer 1

SELECT * FROM x WHERE Column3 NOT IN 
  (SELECT Column3 FROM x GROUP BY Column3 HAVING COUNT(*) > 1)