Question

如果未找到任何值，以下查询将返回NULL。如何在这两个内容中分别添加If，以便Null然后Not Found或其他方式返回查询结果？

SET @id = 26;
SELECT 
(SELECT id  FROM devTable WHERE id <= @id AND country = 'US' ORDER BY id DESC LIMIT 9,1) AS `prev`,
(SELECT id  FROM devTable WHERE id >= @id AND country = 'US' ORDER BY id ASC  LIMIT 1,1) AS `next`

Answer 1

使用IFNULL()：

SET @id = 26;
SELECT 
IFNULL(
  (SELECT id FROM devTable WHERE id <= @id AND country = 'US' ORDER BY id DESC LIMIT 9,1),
  'Not Found') AS prev,
IFNULL(
  (SELECT id FROM devTable WHERE id >= @id AND country = 'US' ORDER BY id ASC  LIMIT 1,1),
  'Not Found') AS next

Answer 2

查找T-SQL Exists命令。

像：

IF EXISTS( SELECT STUFF FROM JUNK WHERE ITEMS=5) THEN
BEGIN
SELECT "HAVE JUNK"  -- OR PRINT, SET, ...
END
ELSE
BEGIN
SELECT "SORRY, DON'T HAVE JUNK" -- OR PRINT, SET, ...
END
END

如何向此查询添加If Else End If

2 个答案: