如何在SQL SELECT中执行IF ... THEN？

Question

我如何IF...THEN在SQL SELECT声明中执行？

例如:

SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product

Answer 1

该CASE语句最接近SQL中的IF,并且在所有版本的SQL Server上都受支持

SELECT CAST(
             CASE
                  WHEN Obsolete = 'N' or InStock = 'Y'
                     THEN 1
                  ELSE 0
             END AS bit) as Saleable, *
FROM Product

你只需要做CAST结果如果你想把结果作为一个布尔值,如果你对a感到满意int,这可行:

SELECT CASE
            WHEN Obsolete = 'N' or InStock = 'Y'
               THEN 1
               ELSE 0
       END as Saleable, *
FROM Product

CASE语句可以嵌入到其他CASE语句中,甚至包含在聚合中.

SQL Server Denali(SQL Server 2012)添加了IIF语句,该语句也可用于访问 :( Martin Smith指出)

SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product

Answer 2

在这种情况下,case语句是你的朋友,并采用以下两种形式之一:

简单的案例:

SELECT CASE <variable> WHEN <value>      THEN <returnvalue>
                       WHEN <othervalue> THEN <returnthis>
                                         ELSE <returndefaultcase>
       END AS <newcolumnname>
FROM <table>

扩展案例:

SELECT CASE WHEN <test>      THEN <returnvalue>
            WHEN <othertest> THEN <returnthis>
                             ELSE <returndefaultcase>
       END AS <newcolumnname>
FROM <table>

您甚至可以将case语句放在order by子句中,以实现真正的花哨排序.

Answer 3

从SQL Server 2012,您可以使用此IIF功能.

SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Salable, *
FROM   Product

这实际上只是一种简写(尽管不是标准的SQL)写作方式CASE.

与扩展CASE版本相比,我更喜欢简洁.

双方IIF()并CASE解决作为SQL语句中的表达式,只能在使用明确的地方.

CASE表达式不能用于控制Transact-SQL语句,语句块,用户定义函数和存储过程的执行流程.

如果这些限制无法满足您的需求(例如需要根据某些条件返回不同形状的结果集),那么SQL Server也会有一个过程IF关键字.

IF @IncludeExtendedInformation = 1
  BEGIN
      SELECT A,B,C,X,Y,Z
      FROM   T
  END
ELSE
  BEGIN
      SELECT A,B,C
      FROM   T
  END

但是,有时必须注意避免使用这种方法的参数嗅探问题.

Answer 4

您可以在SQL CASE语句的强大功能中找到一些不错的示例,我认为您可以使用的语句将是这样的(来自4guysfromrolla):

SELECT
    FirstName, LastName,
    Salary, DOB,
    CASE Gender
        WHEN 'M' THEN 'Male'
        WHEN 'F' THEN 'Female'
    END
FROM Employees

Answer 5

使用CASE.像这样的东西.

SELECT Salable =
        CASE Obsolete
        WHEN 'N' THEN 1
        ELSE 0
    END

Answer 6

SELECT  
(CASE 
     WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES'
                                            ELSE 'NO' 
 END) as Salable
, * 
FROM Product

Answer 7

 SELECT
   CASE 
      WHEN OBSOLETE = 'N' or InStock = 'Y' THEN 'TRUE' 
      ELSE 'FALSE' 
   END AS Salable,
   * 
FROM PRODUCT

Answer 8

Microsoft SQL Server(T-SQL)

在选择使用中:

select case when Obsolete = 'N' or InStock = 'Y' then 'YES' else 'NO' end

在where子句中,使用:

where 1 = case when Obsolete = 'N' or InStock = 'Y' then 1 else 0 end

Answer 9

从这个环节中,我们可以uderstand IF THEN ELSE在IF THEN ELSE:

IF EXISTS(SELECT *
          FROM   Northwind.dbo.Customers
          WHERE  CustomerId = 'ALFKI')
  PRINT 'Need to update Customer Record ALFKI'
ELSE
  PRINT 'Need to add Customer Record ALFKI'

IF EXISTS(SELECT *
          FROM   Northwind.dbo.Customers
          WHERE  CustomerId = 'LARSE')
  PRINT 'Need to update Customer Record LARSE'
ELSE
  PRINT 'Need to add Customer Record LARSE' 

这对T-SQL来说不够好吗？

Answer 10

SQL Server中简单的if-else语句:

DECLARE @val INT;
SET @val = 15;

IF @val < 25
PRINT 'Hi Ravi Anand';
ELSE
PRINT 'By Ravi Anand.';

GO

在SQL Server中嵌套If ... else语句 -

DECLARE @val INT;
SET @val = 15;

IF @val < 25
PRINT 'Hi Ravi Anand.';
ELSE
BEGIN
IF @val < 50
  PRINT 'what''s up?';
ELSE
  PRINT 'Bye Ravi Anand.';
END;

GO

Answer 11

使用CASE声明:

SELECT CASE
       WHEN (Obsolete = 'N' OR InStock = 'Y')
       THEN 'Y'
       ELSE 'N'
END as Available

etc...

Answer 12

使用纯位逻辑:

DECLARE @Product TABLE (
    id INT PRIMARY KEY IDENTITY NOT NULL
   ,Obsolote CHAR(1)
   ,Instock CHAR(1)
)

INSERT INTO @Product ([Obsolote], [Instock])
    VALUES ('N', 'N'), ('N', 'Y'), ('Y', 'Y'), ('Y', 'N')

;
WITH cte
AS
(
    SELECT
        'CheckIfInstock' = CAST(ISNULL(NULLIF(ISNULL(NULLIF(p.[Instock], 'Y'), 1), 'N'), 0) AS BIT)
       ,'CheckIfObsolote' = CAST(ISNULL(NULLIF(ISNULL(NULLIF(p.[Obsolote], 'N'), 0), 'Y'), 1) AS BIT)
       ,*
    FROM
        @Product AS p
)
SELECT
    'Salable' = c.[CheckIfInstock] & ~c.[CheckIfObsolote]
   ,*
FROM
    [cte] c

请参阅工作演示:如果没有MSSQL中的情况

首先,您需要计算所选条件的值case和true.这里有两个NULLIF:

for true: ISNULL(NULLIF(p.[Instock], 'Y'), 1)
for false: ISNULL(NULLIF(p.[Instock], 'N'), 0)

组合在一起得到1或0.接下来使用按位运算符.

这是最WYSIWYG方法.

Answer 13

SQL Server 2012中添加了一个新功能IIF(我们可以简单地使用):

SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product

Answer 14

SELECT 1 AS Saleable, *
  FROM @Product
 WHERE ( Obsolete = 'N' OR InStock = 'Y' )
UNION
SELECT 0 AS Saleable, *
  FROM @Product
 WHERE NOT ( Obsolete = 'N' OR InStock = 'Y' )

Answer 15

SELECT CASE WHEN profile.nrefillno = 0 THEN 'N' ELSE 'R'END as newref
From profile

Answer 16

case statement some what similar to if in SQL server

SELECT CASE 
            WHEN Obsolete = 'N' or InStock = 'Y' 
               THEN 1 
               ELSE 0 
       END as Saleable, * 
FROM Product

Answer 17

这不是一个答案,只是我工作中使用的CASE语句的一个例子.它有一个嵌套的CASE语句.现在你知道为什么我的眼睛交叉了.

 CASE orweb2.dbo.Inventory.RegulatingAgencyName
    WHEN 'Region 1'
        THEN orweb2.dbo.CountyStateAgContactInfo.ContactState
    WHEN 'Region 2'
        THEN orweb2.dbo.CountyStateAgContactInfo.ContactState
    WHEN 'Region 3'
        THEN orweb2.dbo.CountyStateAgContactInfo.ContactState
    WHEN 'DEPT OF AGRICULTURE'
        THEN orweb2.dbo.CountyStateAgContactInfo.ContactAg
    ELSE (
            CASE orweb2.dbo.CountyStateAgContactInfo.IsContract
                WHEN 1
                    THEN orweb2.dbo.CountyStateAgContactInfo.ContactCounty
                ELSE orweb2.dbo.CountyStateAgContactInfo.ContactState
                END
            )
    END AS [County Contact Name]

Answer 18

如果您是第一次将结果插入表中,而不是将结果从一个表传输到另一个表,则可以在Oracle 11.2g中使用:

INSERT INTO customers (last_name, first_name, city)
    SELECT 'Doe', 'John', 'Chicago' FROM dual
    WHERE NOT EXISTS 
        (SELECT '1' from customers 
            where last_name = 'Doe' 
            and first_name = 'John'
            and city = 'Chicago');

Answer 19

作为CASE语句表的替代解决方案,可以使用驱动方法.

DECLARE @Product TABLE (ID INT, Obsolete VARCHAR(10), InStock VARCHAR(10))
INSERT INTO @Product VALUES
(1,'N','Y'),
(2,'A','B'),
(3,'N','B'),
(4,'A','Y')

SELECT P.* , ISNULL(Stmt.Saleable,0) Saleable
FROM
    @Product P
    LEFT JOIN
        ( VALUES
            ( 'N', 'Y', 1 )
        ) Stmt (Obsolete, InStock, Saleable)
        ON  P.InStock = Stmt.InStock OR P.Obsolete = Stmt.Obsolete

结果:

ID          Obsolete   InStock    Saleable
----------- ---------- ---------- -----------
1           N          Y          1
2           A          B          0
3           N          B          1
4           A          Y          1

Answer 20

SELECT CASE WHEN Obsolete = 'N' or InStock = 'Y' THEN 1 ELSE 0 
             END AS Saleable, * 
FROM Product

Answer 21

使用 SQL CASE 就像普通的 If / Else 语句一样。在下面的查询中，如果过时值 = 'N' 或 InStock 值 = 'Y'，则输出将为 1。否则输出将为 0。然后我们将该 0 或 1 值放在可销售列下。

SELECT
      CASE
           WHEN obsolete = 'N' OR InStock = 'Y'
          THEN 1
        ELSE 0
      END AS Salable
      , *
FROM PRODUCT

Answer 22

对于那些使用SQL Server 2012的用户,IIF是一个已添加的功能,可作为Case语句的替代方案.

SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Salable, *
FROM   Product 

Answer 23

  SELECT IIF(Obsolete = 'N' OR InStock = 'Y',1,0) AS Saleable, * FROM Product

Answer 24

问题：

SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product

美国国家标准协会：

Select 
  case when p.Obsolete = 'N' 
  or p.InStock = 'Y' then 1 else 0 end as Saleable, 
  p.* 
FROM 
  Product p;

在这种情况下，使用别名p将有助于防止出现问题。

Answer 25

您可以有两种选择来实际实施：

1. 使用从 SQL Server 2012 引入的 IIF：

   SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product
   

2. 使用Select Case：

   SELECT CASE
       WHEN Obsolete = 'N' or InStock = 'Y'
           THEN 1
           ELSE 0
       END as Saleable, *
       FROM Product
   

Answer 26

SELECT
if((obsolete = 'N' OR instock = 'Y'), 1, 0) AS saleable, *
FROM
product;