How do I perform an IF…THEN in an SQL SELECT?

Question

How do I perform an IF...THEN in an SQL SELECT statement?

For example:

SELECT IF(Obsolete = \'N\' OR InStock = \'Y\' ? 1 :          


        

Answer 1

This isn't an answer, just an example of a CASE statement in use where I work. It has a nested CASE statement. Now you know why my eyes are crossed.

 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 2

As an alternative solution to the CASE statement, a table-driven approach can be used:

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

Result:

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

Answer 3

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

Answer 4

The case statement is your friend in this situation, and takes one of two forms:

The simple case:

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

The extended case:

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

You can even put case statements in an order by clause for really fancy ordering.

Answer 5

You can use Case Statement:

Select 
Case WHEN (Obsolete = 'N' or InStock = 'Y') THEN 1 ELSE 0 END Saleable,
Product.*
from Product

Answer 6

I like the use of the CASE statements but the question asked for an IF statement in the SQL Select. What I've used in the past has been:

SELECT

   if(GENDER = "M","Male","Female") as Gender

FROM ...

It's like the excel or sheets IF statements where there is a conditional followed by the true condition and then the false condition:

if(condition, true, false)

Furthermore, you can nest the if statements (but then use should use a CASE :-)

(Note: this works in MySQLWorkbench but may not work in other platforms)