How do I perform an IF…THEN in an SQL SELECT?
我如何执行在
例如:
1 | SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product |
1 2 3 4 5 6 7 | SELECT CAST( CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS bit) AS Saleable, * FROM Product |
。
如果希望结果为布尔值,则只需执行
1 2 3 4 5 6 | SELECT CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS Saleable, * FROM Product |
SQL Server Denali(SQL Server 2012)添加了IIF语句,该语句在Access中也可用(由Martin Smith指出):
1 | SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Saleable, * FROM Product |
。
案例陈述是您在这种情况下的朋友,采用两种形式之一:
简单的例子:
1 2 3 4 5 | SELECT CASE <variable> WHEN <value> THEN <returnvalue> WHEN <othervalue> THEN <returnthis> ELSE <returndefaultcase> END AS <newcolumnname> FROM <table> |
。
扩展案例:
1 2 3 4 5 | SELECT CASE WHEN <test> THEN <returnvalue> WHEN <othertest> THEN <returnthis> ELSE <returndefaultcase> END AS <newcolumnname> FROM <table> |
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您甚至可以将case语句放在order by子句中,以便进行真正奇特的排序。
在SQL Server 2012中,您可以使用
1 2 | SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Salable, * FROM Product |
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这实际上只是编写
与扩展的
The CASE expression cannot be used to control the flow of execution of
Transact-SQL statements, statement blocks, user-defined functions, and
stored procedures.
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如果这些限制不能满足您的需求(例如,需要根据某些条件返回不同形状的结果集),那么SQL Server也有一个过程性的
1 2 3 4 5 6 7 8 9 10 | IF @IncludeExtendedInformation = 1 BEGIN SELECT A,B,C,X,Y,Z FROM T END ELSE BEGIN SELECT A,B,C FROM T END |
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但是,有时必须小心避免使用这种方法时出现参数嗅探问题。
您可以在SQL case语句的强大功能中找到一些很好的示例,我认为您可以使用的语句如下(来自4Guysfromrolla):
1 2 3 4 5 6 7 8 | SELECT FirstName, LastName, Salary, DOB, CASE Gender WHEN 'M' THEN 'Male' WHEN 'F' THEN 'Female' END FROM Employees |
。
用例。像这样。
1 2 3 4 5 | SELECT Salable = CASE Obsolete WHEN 'N' THEN 1 ELSE 0 END |
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1 2 3 4 5 6 7 | SELECT (CASE WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES' ELSE 'NO' END) AS Salable , * FROM Product |
1 2 3 4 5 6 7 | SELECT CASE WHEN OBSOLETE = 'N' OR InStock = 'Y' THEN 'TRUE' ELSE 'FALSE' END AS Salable, * FROM PRODUCT |
Microsoft SQL Server(T-SQL)
在
1 | SELECT CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 'YES' ELSE 'NO' END |
在
1 | WHERE 1 = CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END |
。
通过这个链接,我们可以理解T-SQL中的
1 2 3 4 5 6 7 8 9 10 11 12 13 | 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' |
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这对T-SQL来说还不够好吗?
SQL Server中的简单if-else语句:
1 2 3 4 5 6 7 8 9 | DECLARE @val INT; SET @val = 15; IF @val < 25 PRINT 'Hi Ravi Anand'; ELSE PRINT 'By Ravi Anand.'; GO |
。
SQL Server中嵌套的if…else语句-
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | 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 |
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使用纯位逻辑:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | 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 |
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请参见工作演示:如果没有,则SQL Server中的
首先,您需要计算所选条件下的
1 2 | FOR TRUE: ISNULL(NULLIF(p.[Instock], 'Y'), 1) FOR FALSE: ISNULL(NULLIF(p.[Instock], 'N'), 0) |
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加在一起得到1或0。接下来使用位运算符。
这是最WYSIWYG的方法。
在SQL Server 2012中添加了一个新功能iif(我们可以简单地使用它):
1 | SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product |
使用案例陈述:
1 2 3 4 5 6 7 | SELECT CASE WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'Y' ELSE 'N' END AS Available etc... |
1 2 3 4 5 6 7 | 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' ) |
1 2 | SELECT CASE WHEN profile.nrefillno = 0 THEN 'N' ELSE 'R'END AS newref FROM profile |
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1 2 3 4 5 6 7 8 | 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 |
这不是答案,只是在我工作的地方使用的一个案例陈述的例子。它有一个嵌套的case语句。现在你知道为什么我的眼睛是交叉的。
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 | 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] |
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如果您是第一次将结果插入到表中,而不是将结果从一个表传输到另一个表中,这在Oracle 11.2g中有效:
1 2 3 4 5 6 7 | 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'); |
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作为
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | 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 |
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结果:
1 2 3 4 5 6 | ID Obsolete InStock Saleable ----------- ---------- ---------- ----------- 1 N Y 1 2 A B 0 3 N B 1 4 A Y 1 |
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1 2 3 | SELECT CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS Saleable, * FROM Product |
1 | SELECT IIF(Obsolete = 'N' OR InStock = 'Y',1,0) AS Saleable, * FROM Product |
对于那些使用SQL Server 2012的用户,IIF是一个已经添加的功能,可以作为case语句的替代。
1 2 | SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Salable, * FROM Product |
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您可以有两种选择来实际实现:
使用从SQL Server 2012引入的IIF:
1 | SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product |
使用
1 2 3 4 5 6 | SELECT CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN 1 ELSE 0 END AS Saleable, * FROM Product |
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问题:
1 | SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product |
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美国国家标准协会:
1 2 3 4 5 6 | SELECT CASE WHEN p.Obsolete = 'N' OR p.InStock = 'Y' THEN 1 ELSE 0 END AS Saleable, p.* FROM Product p; |
使用别名(在本例中为
1 2 3 4 5 6 7 | SELECT CAST( CASE WHEN Obsolete = 'N' OR InStock = 'Y' THEN ELSE 0 END AS bit ) AS Saleable, * FROM Product |