查詢中的行固定值

Question

考慮這個SQL：

SELECT c1 AS C1, 
     1 AS NO 
FROM t1 
WHERE c1 = 'abc' 
UNION 
SELECT c1 AS C1, 
     2 AS NO 
FROM t2 
ORDER BY NO 

，你可能會注意到自己，工會之前第一個SELECT語句只是一個旁路到一個新值添加到第二個查詢返回的列表。

有沒有辦法在查詢中不涉及t1？這是我的感覺，這是沒有必要的，但無法用這個查詢做得更好。

結果：

C1 |NO 
--------------- 
abc |1 
def |2 
ghi |2 
jkl |2 
mno |2 
etc |2 
--------------- 

Answer 1

當您添加1 AS NO，你可以添加'abc' AS C1：

SELECT 'abc' AS C1, 
     1 AS NO 
    FROM DUAL 
UNION 
SELECT c1 AS C1, 
     2 AS NO 
    FROM t2 
ORDER BY NO;