49

我有一个 select 语句，它将返回 2 列。

ID | IDParent

然后在我的程序中我必须测试if IDParent is < 1 then use ID ELSE use IDParent

有没有办法在 SQL 中使用类似 If Else 的条件来仅返回单个值？

4

11 回答 11

103

您可以使用CASE

SELECT   ...,
         CASE WHEN IDParent < 1 THEN ID ELSE IDPArent END AS ColumnName,
         ...
FROM     tableName
于 2012-11-23T09:55:27.367 回答
30

在这里，使用CASE Statement并查找结果：

select (case when condition1 then result1
             when condition2 then result2
             else result3
             end) as columnname from tablenmae:

例如：

select (CASE WHEN IDParent< 1 then ID 
             else IDParent END) as columnname
from tablenmae
于 2012-11-23T09:59:34.793 回答
23 
SELECT CASE WHEN IDParent < 1 
            THEN ID 
            ELSE IDParent 
       END AS colname 
FROM yourtable
于 2012-11-23T09:55:31.317 回答
4

查询将如下所示

SELECT (CASE WHEN tuLieuSo is null or tuLieuSo=''
            THEN 'Chưa có đĩa' 
            ELSE 'Có đĩa' End) AS tuLieuSo,moTa
FROM [gPlan_datav3_SQHKTHN].[dbo].[gPlan_HoSo]
于 2014-10-06T03:56:59.017 回答
2

sql server 2012

  with
  student as 
(select sid,year from (
values (101,5),(102,5),(103,4),(104,3),(105,2),(106,1),(107,4)
) as student(sid,year)
)
select iif(year=5,sid,year) as myCol,* from student


 myCol  sid year
101 101 5
102 102 5
4   103 4
3   104 3
2   105 2
1   106 1
4   107 4
于 2014-10-11T09:57:38.053 回答
2

您可以在查询下使用简单if的语句，select如下所述

if(some_condition,if_satisfied,not_satisfied)

SELECT IF(IDParent < 1,ID,IDParent)  FROM yourTable ;
于 2019-04-17T09:29:05.640 回答
1

这是一些使用示例CASE WHEN

SELECT 
    CASE WHEN A > 1 THEN
            'Greater than 1'
    END  
FROM TRIANGLES

.

SELECT 
    CASE WHEN A > 1 THEN
            A
    END  
FROM TRIANGLES

.

SELECT 
    CASE WHEN A > 1 and B > 1 THEN
            'Greater than 1'
    END  
FROM TRIANGLES

.

SELECT 
    CASE WHEN A > 1 THEN
            'greater than 1'
         ELSE
            'less than 1'
    END  
FROM TRIANGLES

.

SELECT 
    CASE WHEN A > 1 THEN
            'greater than 1'
         ELSE CASE WHEN A >= 0 THEN
                      'greater than or equal 0'
                   ELSE
                      'less than 0'
              END        
    END  
FROM TRIANGLES;

希望这可以帮助

于 2018-12-28T06:17:15.653 回答
1

这里有两种方式“IF”或“CASE”。

SELECT IF(COLUMN_NAME = "VALUE", "VALUE_1", "VALUE_2") AS COLUMN_NAME 
FROM TABLE_NAME;

或者

SELECT (CASE WHEN COLUMN_NAME = "VALUE" THEN 'VALUE_1' ELSE 'VALUE_2' END) AS COLUMN_NAME 
FROM TABLE_NAME;
于 2020-02-17T10:11:18.780 回答
0

您还可以使用联合构造。我不确定 CASE 是否是一个常见的 SQL 构造......

SELECT ID FROM tabName WHERE IDParent<1 OR IDParent IS NULL
UNION 
SELECT IDParent FROM tabName WHERE IDParent>1
于 2012-11-23T10:17:44.787 回答
0 
select 
CASE WHEN IDParent is < 1 then ID else IDParent END as colname 
from yourtable
于 2012-11-23T11:17:58.293 回答
0

我对此结果有疑问：

SELECT Top 3
 id,
 Paytype
 FROM dbo.OrderExpresses
 WHERE CreateDate > '2018-04-08'

结果是：

22082   1
22083   2
22084   1

我想在查询中将代码更改为字符串，所以我使用此代码：

SELECT TOP 3
 id,
 CASE WHEN Paytype = 1 THEN N'Credit' ELSE N'Cash' END AS PayTypeString
 FROM dbo.OrderExpresses
 WHERE CreateDate > '2018-04-08'

结果是:)

22082   Credit
22083   Cash
22084   Credit
于 2018-04-08T05:37:44.420 回答