IF使用Transact SQL語句

Question

當我執行我的Transact SQL代碼

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' 

我收到以下錯誤：

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

Answer 1

如何只使用COALESCE()？

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

IF是不需要的。

錯誤本身似乎很明顯。有一個在request_unit多行，其中request_id是4357.

Answer 2

嘗試......

這意味着有幾個model_id爲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' 

這也能成爲使用，但@Gordon Lioff的回答是首選

Answer 4

隨着@ GordonLinoff的答案你可以請寫下列內容以獲得列名：

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

Answer 5

您可以這樣做;

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' 

IIFStarting 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'