如何從行和列兩者一起

Question

選擇不同的值，這是一些values.There我的數據庫表有不同的主題名稱從TOPIC1到topic8。 我想從所有這些值訪問不同的主題名稱。 什麼將是它的SQL查詢？

Answer 1

要澄清答案： 使用UNION運算符的SELECT命令會自行返回不同的值。所以不需要DISTINCT關鍵字。

SELECT和UNION ALL也會返回重複值。

Answer 2

使用聯合查詢：

select topic1 as topic from t union 
select topic2 as topic from t union 
select topic3 as topic from t union 
select topic4 as topic from t union 
select topic5 as topic from t union 
select topic6 as topic from t union 
select topic7 as topic from t union 
select topic8 as topic from t; 

如果你不想NULL這樣做，那麼包括WHERE條款：

select topic1 as topic from t where topic1 is not null union 
select topic2 as topic from t where topic2 is not null union 
select topic3 as topic from t where topic3 is not null union 
select topic4 as topic from t where topic4 is not null union 
select topic5 as topic from t where topic5 is not null union 
select topic6 as topic from t where topic6 is not null union 
select topic7 as topic from t where topic7 is not null union 
select topic8 as topic from t where topic8 is not null; 

Answer 3

試試這個：

SELECT DISTINCT topic1 
FROM TABLE 
UNION 
SELECT DISTINCT topic2 
FROM TABLE 
SELECT DISTINCT topic3 
FROM TABLE 

所有重複必要的欄目