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[英]How to select unique values from one column based on a value in another column?
[英]How to select just unique values into a mysql table based on the value in one column?
我有一個名為x的表
這是表x中的示例數據
Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3
一_ _ __ __ _ _ __ __ _ _ __ ___ b _ _ __ __ _ _ __ __ _ _ __ __ _ __ _c
a2_ _ __ _ __ __ _ _ _ __ __ _ _ _ B2 __ _ __ _ __ __ _ _ _ __ __ _ __ _c
a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2
a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3
我在新表中需要的結果是:
Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3
a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2
a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3
我嘗試將值導入到新表中並在第3列上應用唯一索引,但我得到的結果是
Column1_ _ __ _ __ _ __ _ _ Column2_ _ __ _ __ _ __ _ ___ Column3
a_ _ __ _ __ _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c
a3_ _ __ _ __ _ __ _ __ _ _ _ _ _ b3 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ c2
a4_ _ __ _ __ _ __ _ __ _ _ _ _ b4 _ __ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ ___ _c3
SELECT * FROM x WHERE Column3 NOT IN
(SELECT Column3 FROM x GROUP BY Column3 HAVING COUNT(*) > 1)
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