T-SQL筆記28_Union跟Union All

 

在查詢中有時候我們可能會有多組子查詢

可能欄位對應都一致

但想合併為同一張資料表結果集合時候

就可以透過Union 或 Union All來達成

其中Union 會做distinct去除重複的只留唯一

Union All則不會去除重複的全部保留

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SELECT 'B' AS COL UNION ALL SELECT 'A' AS Val UNION ALL SELECT 'B' AS Result SELECT 'B' AS COL UNION SELECT 'A' AS Val UNION SELECT 'B' AS Result

Ref:

What is the difference between UNION and UNION ALL

https://dataschool.com/learn-sql/what-is-the-difference-between-union-and-union-all/