1775

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

For example:

SELECT IF(Obsolete = 'N' OR InStock = 'Y' ? 1 : 0) AS Saleable, * FROM Product
DineshDB
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Eric Labashosky
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29 Answers29

2021

The CASE statement is the closest to IF in SQL and is supported on all versions of SQL Server.

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

You only need to use the CAST operator if you want the result as a Boolean value. If you are happy with an int, this works:

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

CASE statements can be embedded in other CASE statements and even included in aggregates.

SQL Server Denali (SQL Server 2012) adds the IIF statement which is also available in access (pointed out by Martin Smith):

SELECT IIF(Obsolete = 'N' or InStock = 'Y', 1, 0) as Saleable, * FROM Product
Hameed Syed
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Darrel Miller
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    Beware of dirty secrets of CASE/IIF: https://sqlperformance.com/2014/06/t-sql-queries/dirty-secrets-of-the-case-expression –  Jan 27 '17 at 12:21
  • I implemented this on a SQLite3 database, following this tutorial: https://www.sqlitetutorial.net/sqlite-functions/sqlite-iif/ – ftani Sep 14 '22 at 14:08
364

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.

Christoph
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Jonathan
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314

From SQL Server 2012 you can use the IIF function for this.

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

This is effectively just a shorthand (albeit not standard SQL) way of writing CASE.

I prefer the conciseness when compared with the expanded CASE version.

Both IIF() and CASE resolve as expressions within a SQL statement and can only be used in well-defined places.

The CASE expression cannot be used to control the flow of execution of Transact-SQL statements, statement blocks, user-defined functions, and stored procedures.

If your needs can not be satisfied by these limitations (for example, a need to return differently shaped result sets dependent on some condition) then SQL Server does also have a procedural IF keyword.

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

Care must sometimes be taken to avoid parameter sniffing issues with this approach however.

Peter Mortensen
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Martin Smith
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113

You can find some nice examples in The Power of SQL CASE Statements, and I think the statement that you can use will be something like this (from 4guysfromrolla):

SELECT
    FirstName, LastName,
    Salary, DOB,
    CASE Gender
        WHEN 'M' THEN 'Male'
        WHEN 'F' THEN 'Female'
    END
FROM Employees
Aaron Bertrand
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sven
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87

Use CASE. Something like this.

SELECT Salable =
        CASE Obsolete
        WHEN 'N' THEN 1
        ELSE 0
    END
palehorse
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62
SELECT  
(CASE 
     WHEN (Obsolete = 'N' OR InStock = 'Y') THEN 'YES'
                                            ELSE 'NO' 
 END) as Salable
, * 
FROM Product
Zyku
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John Sheehan
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51

From this link, we can understand IF THEN ELSE in T-SQL:

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' 

Isn't this good enough for T-SQL?

Peter Mortensen
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Ken
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    This isn't what the requester wanted, but is very useful to know that you can use if statements *outside* a select statement. – Jonathan Apr 10 '13 at 08:06
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    EXISTS is good because it kicks out of the search loop if item is found. A COUNT runs until the end of table rows. Nothing to do with question, but something to know. – JustJohn Feb 11 '16 at 21:12
51

Microsoft SQL Server (T-SQL)

In a select, use:

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

In a where clause, use:

where 1 = case when Obsolete = 'N' or InStock = 'Y' then 1 else 0 end
Peter Mortensen
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user7658
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50
 SELECT
   CASE 
      WHEN OBSOLETE = 'N' or InStock = 'Y' THEN 'TRUE' 
      ELSE 'FALSE' 
   END AS Salable,
   * 
FROM PRODUCT
Santiago Cepas
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33

Simple if-else statement in SQL Server:

DECLARE @val INT;
SET @val = 15;

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

GO

Nested If...else statement in SQL Server -

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
Peter Mortensen
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Ravi Anand
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25

Use a CASE statement:

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

etc...
Krizzy
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24

A new feature, IIF (that we can simply use), was added in SQL Server 2012:

SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product
twoleggedhorse
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sandeep rawat
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    This answer repeats (with less detail) what was [already provided in the answer by Martin Smith](https://stackoverflow.com/a/6769805/4515489) several years ago. – jk7 Oct 31 '18 at 19:47
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    @jk7 this was the first answer to the question . – sandeep rawat Nov 01 '18 at 02:46
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    Not from what I see. It says your answer was posted Apr 26 '16 and Martin's was posted Jul 20 '11. – jk7 Nov 02 '18 at 14:40
23

Use pure bit logic:

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

See working demo: if then without case in SQL Server.

For start, you need to work out the value of true and false for selected conditions. Here comes two NULLIF:

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

combined together gives 1 or 0. Next use bitwise operators.

It's the most WYSIWYG method.

Peter Mortensen
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Tomasito
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    -1 for Code Obfuscation. Seriously, this is about as far from WYSIWYG as you can get! A ruddy unreadable mess, and if I had to work on your code, I would be cursing all day long... sorry :-/ – Riegardt Steyn Jun 22 '13 at 08:47
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    @Heliac put cte part in View and you will never see the mess. For long and complicated AND, OR, NOT it it more readable than CASE (that part outside cte of course). – Tomasito Jun 23 '13 at 09:52
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    I've given this a +1 for the neatness, once it's in a cte, but note that the answer is currently wrong for the question. You need an '|' not an '&'. – Mark Hurd Nov 16 '16 at 00:19
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    Totally agree with @Heliac. While it is syntactically correct and works fine it is just not easily supportable. Putting it in a CTE will just move that piece of un-readable code somewhere else. – objectNotFound Nov 24 '17 at 17:04
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    The table method of checking combination could have its advantages. Using a table variable and joining it to the existing query could provide a set-based solution without a case. This answer is a poor example, but the table idea itself has merit. – Suncat2000 Nov 30 '18 at 13:19
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    `NULLIF` link from Microsoft is expired. here is new working link: https://learn.microsoft.com/en-us/sql/t-sql/language-elements/nullif-transact-sql?view=sql-server-2017 Updated in answer. – abdul qayyum Feb 17 '19 at 10:18
18
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' )
onedaywhen
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16
SELECT CASE WHEN profile.nrefillno = 0 THEN 'N' ELSE 'R'END as newref
From profile
Mohammad Atiour Islam
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13
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
Chanukya
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13

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]
NzGuy
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JustJohn
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    The edit that reformatted the Case statements is all fine and dandy and makes it more understandable but the SQL would still all lump up in the view that is using it. – JustJohn Oct 12 '16 at 16:30
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    I'm just wandering why `CASE` become upvoted and marked as a answer instead of the `IF` which should have been the answer, like this one, this is still a `CASE`statement, not an `IF`. – Mr.J Mar 22 '17 at 07:16
  • @Mr.J: though not my answer, a 'case' generalizes an 'if-then-else' (from 2 cases to many) – JosephDoggie Oct 02 '18 at 16:40
10

If you're inserting results into a table for the first time, rather than transferring results from one table to another, this works in Oracle 11.2g:

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');
Peter Mortensen
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10

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
Peter Mortensen
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Serkan Arslan
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9
SELECT CASE WHEN Obsolete = 'N' or InStock = 'Y' THEN 1 ELSE 0 
             END AS Saleable, * 
FROM Product
8

You can have two choices for this to actually implement:

  1. Using IIF, which got introduced from SQL Server 2012:

    SELECT IIF ( (Obsolete = 'N' OR InStock = 'Y'), 1, 0) AS Saleable, * FROM Product
    
  2. Using Select Case:

    SELECT CASE
        WHEN Obsolete = 'N' or InStock = 'Y'
            THEN 1
            ELSE 0
        END as Saleable, *
        FROM Product
    
Peter Mortensen
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8

Using SQL CASE is just like normal If / Else statements. In the below query, if obsolete value = 'N' or if InStock value = 'Y' then the output will be 1. Otherwise the output will be 0. Then we put that 0 or 1 value under the Salable Column.

SELECT
      CASE
           WHEN obsolete = 'N' OR InStock = 'Y'
          THEN 1
        ELSE 0
      END AS Salable
      , *
FROM PRODUCT
Peter Mortensen
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Tharuka Madumal
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    It is just like normal If / Else statements. If obsolete value = 'N' or If InStock value = 'Y' Then Output will be 1. Otherwise output will be 0. – Tharuka Madumal Feb 18 '20 at 11:22
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    Thank you. Please [Edit](https://stackoverflow.com/posts/60278997/edit) your post to add this explanation. Like: The `If..Then...Else..` statements usage in `SQL` as follows.... –  Feb 18 '20 at 11:39
  • "Salable"? Isn't it "Saleable"? – Peter Mortensen Sep 17 '22 at 23:32
5

Question:

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

ANSI:

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

Using aliases -- p in this case -- will help prevent issues.

Bikramjeet Singh
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David Cohn
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  • What do you mean by *"ANSI"*? ANSI SQL? What version? 1992? 2011? As opposed what, for example? What was it tested on? Please respond by [editing (changing) your answer](https://stackoverflow.com/posts/53121744/edit), not here in comments (****** ***without*** ****** "Edit:", "Update:", or similar - the answer should appear as if it was written today). – Peter Mortensen Sep 23 '22 at 14:58
5
SELECT
if((obsolete = 'N' OR instock = 'Y'), 1, 0) AS saleable, *
FROM
product;
The AG
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4

For those who uses SQL Server 2012, IIF is a feature that has been added and works as an alternative to Case statements.

SELECT IIF(Obsolete = 'N' OR InStock = 'Y', 1, 0) AS Salable, *
FROM   Product 
demongolem
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Dibin
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    This answer repeats (with less detail) what was [already provided in the answer by Martin Smith](https://stackoverflow.com/a/6769805/4515489) several years ago. – jk7 Oct 31 '18 at 19:44
3

It will be something like that:

SELECT OrderID, Quantity,
CASE
    WHEN Quantity > 30 THEN "The quantity is greater than 30"
    WHEN Quantity = 30 THEN "The quantity is 30"
    ELSE "The quantity is under 30"
END AS QuantityText
FROM OrderDetails;
Muhammad Awais
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    Can we use QuantityText value in where condition in a query ? for example `SELECT OrderID, Quantity, CASE WHEN Quantity > 30 THEN "The quantity is greater than 30" WHEN Quantity = 30 THEN "The quantity is 30" ELSE "The quantity is under 30" END AS QuantityText FROM OrderDetails WHERE QuantityText = 'The quantity is 30'; ` – Bhavin Thummar Nov 08 '19 at 12:14
3

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 MySQL Workbench, but it may not work on other platforms)

Peter Mortensen
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    [IF FUNCTION](https://dev.mysql.com/doc/refman/8.0/en/control-flow-functions.html) It seems present in MySQL, but not in MSSQL, In MSSQL [IIF](https://learn.microsoft.com/en-us/sql/t-sql/functions/logical-functions-iif-transact-sql?view=sql-server-ver15) can be used since version 2012. – Luuk Aug 01 '20 at 09:15
2

For the sake of completeness, I would add that SQL uses three-valued logic. The expression:

obsolete = 'N' OR instock = 'Y'

Could produce three distinct results:

| obsolete | instock | saleable |
|----------|---------|----------|
| Y        | Y       | true     |
| Y        | N       | false    |
| Y        | null    | null     |
| N        | Y       | true     |
| N        | N       | true     |
| N        | null    | true     |
| null     | Y       | true     |
| null     | N       | null     |
| null     | null    | null     |

So for example if a product is obsolete but you dont know if product is instock then you dont know if product is saleable. You can write this three-valued logic as follows:

SELECT CASE
           WHEN obsolete = 'N' OR instock = 'Y' THEN 'true'
           WHEN NOT (obsolete = 'N' OR instock = 'Y') THEN 'false'
           ELSE NULL
       END AS saleable

Once you figure out how it works, you can convert three results to two results by deciding the behavior of null. E.g. this would treat null as not saleable:

SELECT CASE
           WHEN obsolete = 'N' OR instock = 'Y' THEN 'true'
           ELSE 'false' -- either false or null
       END AS saleable
Salman A
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1

There are multiple conditions.

SELECT

(CASE
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1001' THEN 'DM'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1002' THEN 'GS'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1003' THEN 'MB'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1004' THEN 'MP'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1005' THEN 'PL'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1008' THEN 'DM-27'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1011' THEN 'PB'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1012' THEN 'UT-2'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1013' THEN 'JGC'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1014' THEN 'SB'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1015' THEN 'IR'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1016' THEN 'UT-3'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1017' THEN 'UT-4'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1019' THEN 'KR'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1020' THEN 'SYB-SB'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1021' THEN 'GR'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1022' THEN 'SYB-KP'
WHEN RIGHT((LEFT(POSID,5)),4) LIKE '1026' THEN 'BNS'

  ELSE ''
END) AS OUTLET

FROM matrixcrm.Transact
durlove roy
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  • Why 18? Why not 19? What do all the magic numbers and letter codes mean? For instance, what is "SYB-KP"? Why all the redundancy? An explanation would be in order. E.g., what is the idea/gist? From [the Help Center](https://stackoverflow.com/help/promotion): *"...always explain why the solution you're presenting is appropriate and how it works"*. Please respond by [editing (changing) your answer](https://stackoverflow.com/posts/71934110/edit), not here in comments (********** ***without*** ************ "Edit:", "Update:", or similar - the answer should appear as if it was written today). – Peter Mortensen Sep 17 '22 at 16:58