如何在不满足WHERE条件时选择至少一行的一行？

Question

我有一个非常简单的查询,返回一组行,从下表:

Table1
N1  N2
1   A1
1   A2
2   B1
2   B2
2   B3

我只需要从表中一行(TOP(1))N1 = @X.在所有情况下,我宁愿得到一个特定的N2值,但并非所有情况下N2都会存在一个值N1

例如,以下查询不会返回任何行:

SELECT TOP(1) N1, N2 FROM Table WHERE N1 = 2 AND N2 = 'B4'

我正在寻找一种简单的方法来返回至少1行,即使条件N2 = @N2没有满足.返回哪一行无关紧要,如果该@N2值不存在则任何行都可以.

到目前为止,我已经完成了以下操作,但我想如果有人知道更简单的事情:

;with tmp AS (
SELECT TOP(1) *, 1 AS No FROM Table1 WHERE N1 = @N1 AND N2 = @N2
UNION
SELECT TOP(1) *, 2 AS No FROM Table1 WHERE N1 = @N1
)

SELECT TOP(1) * FROM tmp ORDER BY No

任何帮助将不胜感激

Answer 1

我想你想要order by:

SELECT TOP(1) N1, N2
FROM Table
WHERE N1 = 2 
ORDER BY (CASE WHEN N2 = 'B4' THEN 1 ELSE 2 END);