如何根据一列中的值在mysql表中选择唯一的值？

我有一张名为x的桌子

下面是表x中的示例数据

第1列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第2列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第3栏

ab\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuc

a2\uUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUUCb2\uUUUUUUUUUUUUUUUUUUUUUUUC

a3 a4b4Uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuc3

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

在新表中，我需要的结果是：

第1列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第2列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第3栏

a3 a4b4Uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuc3

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

我尝试将值导入一个新表，并在第3列上应用一个唯一的索引，但结果是

第1列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第2列\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu 第3栏

a\uuuuuuuuuuuuuuuuuuuuuuuuuuuuub\uuuuuuuuuuuuuuuuuuuuuuuu\c

a3 a4b4Uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuc3

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