SQL: IF clause within WHERE clause

Is it possible to use an IF clause within a WHERE clause in MS SQL?

Example:

WHERE
	IF IsNumeric(@OrderNumber) = 1
		OrderNumber = @OrderNumber
	ELSE
		OrderNumber LIKE '%' + @OrderNumber + '%'

Use a CASE statement
UPDATE: The previous syntax (as pointed out by a few people) doesn't work. You can use CASE as follows:

WHERE OrderNumber LIKE
  CASE WHEN IsNumeric(@OrderNumber) = 1 THEN 
    @OrderNumber 
  ELSE
    '%' + @OrderNumber
  END

Or you can use an IF statement like @N. J. Reed points out.

You should be able to do this without any IF or CASE

 WHERE 
   (IsNumeric(@OrderNumber) AND
      (CAST OrderNumber AS VARCHAR) = (CAST @OrderNumber AS VARCHAR)
 OR
   (NOT IsNumeric(@OrderNumber) AND
       OrderNumber LIKE ('%' + @OrderNumber))

Depending on the flavour of SQL you may need to tweak the casts on the order number to an INT or VARCHAR depending on whether implicit casts are supported.

This is a very common technique in a WHERE clause. If you want to apply some "IF" logic in the WHERE clause all you need to do is add the extra condition with an boolean AND to the section where it needs to be applied.

You don't need a IF statement at all.

WHERE
	(IsNumeric(@OrderNumber) = 1 AND OrderNumber = @OrderNumber)
OR (IsNumeric(@OrderNumber) = 0 AND OrderNumber LIKE '%' + @OrderNumber + '%')

There isn't a good way to do this in SQL. Some approaches I have seen:

1. Use CASE combined with boolean operators:

   WHERE OrderNumber = CASE WHEN (IsNumeric(@OrderNumber) = 1) THEN CONVERT(INT, @OrderNumber) ELSE -9999 -- Some numeric value that just cannot exist in the column END OR FirstName LIKE CASE WHEN (IsNumeric(@OrderNumber) = 0) THEN '%' + @OrderNumber ELSE '' END

2. Use IF's outside the SELECT

   IF (IsNumeric(@OrderNumber)) = 1 BEGIN SELECT * FROM Table WHERE @OrderNumber = OrderNumber END ELSE BEGIN SELECT * FROM Table WHERE OrderNumber LIKE '%' + @OrderNumber END

3. Using a long string, compose your SQL statement conditionally, and then use EXEC

The 3rd approach is hideous, but it's almost the only think that works if you have a number of variable conditions like that.

Use a CASE statement instead of IF.

You want the CASE statement

WHERE OrderNumber LIKE
CASE WHEN IsNumeric(@OrderNumber)=1 THEN @OrderNumber ELSE '%' + @OrderNumber END

I think that where...like/=...case...then... can work with Booleans. I am using T-SQL.

Scenario: Let's say you want to get Person-30's hobbies if bool is false, and Person-42's hobbies if bool is true. (According to some, hobby-lookups comprise over 90% of business computation cycles, so pay close attn.).

CREATE PROCEDURE sp_Case
@bool	bit
AS
SELECT Person.Hobbies
FROM Person
WHERE Person.ID = 
	case @bool 
		when 0 
			then 30
		when 1
			then 42
	end;

// an example for using a stored procedure to select users filtered by country and site

CREATE STORED PROCEDURE GetUsers
@CountryId int = null,
@SiteId int = null
AS
BEGIN
SELECT *
		FROM Users
		WHERE
				CountryId  = CASE WHEN ISNUMERIC(@CountryId) = 1 THEN @CountryId ELSE CountryId END AND 
				SiteId	   = CASE WHEN ISNUMERIC(@SiteId) = 1 THEN @SiteId ELSE SiteId END END

> // take from the input countryId AND/OR siteId if exists else don't filter

To clarify some of the logical equivalence solutions.

An if statement

if (a) then b

is logically equivalent to

(!a || b)

It's the first line on the Logical equivalences involving conditional statements section of the Logical equivalence wikipedia article.

To include the else, all you would do is add another conditional

if(a) then b; 
if(!a) then c;

which is logically equivalent to (!a || b) && (a || c)

So using the OP as an example:

IF IsNumeric(@OrderNumber) = 1
    OrderNumber = @OrderNumber
ELSE
    OrderNumber LIKE '%' + @OrderNumber + '%'

the logical equivalent would be:

(IsNumeric(@OrderNumber) <> 1 OR OrderNumber = @OrderNumber)
AND (IsNumeric(@OrderNumber) = 1 OR OrderNumber LIKE '%' + @OrderNumber + '%' )

WHERE (IsNumeric(@OrderNumber) <> 1 OR OrderNumber = @OrderNumber)
AND (IsNumber(@OrderNumber) = 1 OR OrderNumber LIKE '%'
+ @OrderNumber + '%')

> CASE Statement is better option than IF always.

  WHERE  vfl.CreatedDate >= CASE WHEN @FromDate IS NULL THEN vfl.CreatedDate ELSE  @FromDate END
    AND vfl.CreatedDate<=CASE WHEN @ToDate IS NULL THEN vfl.CreatedDate ELSE @ToDate END 

    WHERE OrderNumber LIKE CASE WHEN IsNumeric(@OrderNumber) = 1 THEN @OrderNumber ELSE  '%' + @OrderNumber END

In line case Condition will work properly.

In sql server I had same problem I wanted to use an and statement only if parameter is false and on true I had to show both values true and false so I used it this way

(T.IsPublic = @ShowPublic or  @ShowPublic = 1)

The following example executes a query as part of the Boolean expression and then executes slightly different statement blocks based on the result of the Boolean expression. Each statement block starts with BEGIN and completes with END.

USE AdventureWorks2012;
GO
DECLARE @AvgWeight decimal(8,2), @BikeCount int
IF 
(SELECT COUNT(*) FROM Production.Product WHERE Name LIKE 'Touring-3000%' ) > 5
BEGIN
   SET @BikeCount = 
        (SELECT COUNT(*) 
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%');
   SET @AvgWeight = 
        (SELECT AVG(Weight) 
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%');
   PRINT 'There are ' + CAST(@BikeCount AS varchar(3)) + ' Touring-3000 bikes.'
   PRINT 'The average weight of the top 5 Touring-3000 bikes is ' + CAST(@AvgWeight AS varchar(8)) + '.';
END
ELSE 
BEGIN
SET @AvgWeight = 
        (SELECT AVG(Weight)
         FROM Production.Product 
         WHERE Name LIKE 'Touring-3000%' );
   PRINT 'Average weight of the Touring-3000 bikes is ' + CAST(@AvgWeight AS varchar(8)) + '.' ;
END ;
GO

Using nested IF...ELSE statements The following example shows how an IF … ELSE statement can be nested inside another. Set the @Number variable to 5, 50, and 500 to test each statement.

DECLARE @Number int
SET @Number = 50
IF @Number > 100
   PRINT 'The number is large.'
ELSE 
   BEGIN
      IF @Number < 10
      PRINT 'The number is small'
   ELSE
      PRINT 'The number is medium'
   END ;
GO

If @LstTransDt is Null
				begin
					Set	@OpenQty=0
				end
			else
				begin
				   Select   @OpenQty=IsNull(Sum(ClosingQty),0)  
				   From  ProductAndDepotWiseMonitoring  
				   Where   Pcd=@PCd And PtpCd=@PTpCd And TransDt=@LstTransDt      
			  	end	

See if this helps.

USE AdventureWorks2012;
GO
IF 
(SELECT COUNT(*) FROM Production.Product WHERE Name LIKE 'Touring-3000%' ) > 5
PRINT 'There are more than 5 Touring-3000 bicycles.'
ELSE PRINT 'There are 5 or less Touring-3000 bicycles.' ;
GO