Question

当我执行我的transact SQL代码

时

IF (SELECT model_id FROM request_unit where request_id = '4357') IS NULL
    SELECT part_id FROM request_unit WHERE request_id = '4357'
ELSE
     SELECT model_id FROM request_unit where request_id = '4357'

我收到以下错误：

子查询返回的值超过1。这是不允许的子查询跟随=，！=，＆lt;，＆lt; =，＆gt;，＆gt; =或当子查询用作表达。

Answer 1

如何使用COALESCE()？

SELECT COALESCE(model_id, part_id)
FROM request_unit 
WHERE request_id = '4357';

不需要IF。

错误本身似乎很明显。 request_unit中有多行，request_id为4357。

Answer 2

试试这个......

这意味着model_id

有多个request_id = '4357'

IF Not Exists (SELECT model_id FROM request_unit where request_id = '4357')
    SELECT part_id FROM request_unit WHERE request_id = '4357'
ELSE
     SELECT model_id FROM request_unit where request_id = '4357'

Answer 3

  IF (SELECT top 1 model_id FROM request_unit where request_id = '4357') IS NULL
    SELECT part_id FROM request_unit WHERE request_id = '4357'
ELSE
     SELECT model_id FROM request_unit where request_id = '4357'

这也可以使用，但@Gordon Lioff的答案是首选的

Answer 4

除了@ GordonLinoff的回答，您还可以编写以下内容以获取列名称：

SELECT COALESCE(model_id, part_id) as 'YOURCOLUMNNAME'
FROM request_unit 
WHERE request_id = '4357';

Answer 5

你可以这样做;

COALESCE

SELECT COALESCE(model_id, part_id) FROM request_unit WHERE request_id = '4357'

ISNULL

SELECT ISNULL(model_id, part_id) FROM request_unit WHERE request_id = '4357'

CASE WHEN

SELECT CASE WHEN model_id IS NULL THEN part_id ELSE model_id END FROM request_unit WHERE request_id = '4357'

IIF Starting with 2012

SELECT IIF(model_id IS NULL, part_id, model_id) THEN part_id ELSE model_id END FROM request_unit WHERE request_id = '4357'

带有Transact SQL的IF语句

5 个答案: