5 Ways to Master Dynamic WHERE Clauses in T-SQL

Stop struggling with complex search filters in your stored procedures. This guide breaks down the most effective techniques for building dynamic WHERE clauses in SQL Server.

• COALESCE
• OR Operator
• ISNULL
• CASE
• Dynamic SQL query.

Note - All example I have done with NORTHWIND database

1 . COALESCE.

DECLARE @OrderID int,
                   @ProductID int


SET @OrderID =null
SET @ProductID =null

SELECT [OrderID]
               ,[ProductID]
               ,[UnitPrice]
               ,[Quantity]
               ,[Discount]
FROM [dbo].[OrderDetails]
WHERE OrderID = COALESCE(@OrderID , OrderID)
               AND [ProductID] =COALESCE(@ProductID , [ProductID])

   Find out more about COALESCE

2. OR Operator.

DECLARE @OrderID int,
                   @ProductID int

SET @OrderID =null
SET @ProductID =null

SELECT [OrderID]
                 ,[ProductID]
                 ,[UnitPrice]
                 ,[Quantity]
                 ,[Discount]
FROM    [dbo].[OrderDetails]
WHERE  ((@OrderID IS NULL) OR (OrderID = @OrderID))
                 AND ((@ProductID IS NULL) OR (ProductID =@ProductID))

3. ISNULL.

DECLARE @OrderID int,
                   @ProductID int

SET @OrderID =null
SET @ProductID =null

SELECT [OrderID]
               ,[ProductID]
               ,[UnitPrice]
               ,[Quantity]
               ,[Discount]
 FROM   [dbo].[OrderDetails]
 WHERE OrderID = ISNULL(@OrderID , OrderID)
                AND [ProductID] =ISNULL(@ProductID , [ProductID])

Find out more about ISNULL

4. CASE

 DECLARE @OrderID int,
                    @ProductID int

SET @OrderID =null
SET @ProductID =null

SELECT [OrderID]
             ,[ProductID]
             ,[UnitPrice]
             ,[Quantity]
             ,[Discount]
 FROM [dbo].[OrderDetails]
 WHERE OrderID = CASE WHEN @OrderID IS NOT NULL THEN @OrderID ELSE OrderID                                          END
                                  AND [ProductID] =CASE WHEN @ProductID IS NOT NULL THEN                                                 @ProductID ELSE ProductID END

5. Dynamic SQL Query

DECLARE @OrderID int,
                   @ProductID int ,
                   @DyWhere nvarchar(MAX),
                   @DyQuery nvarchar(MAX)

SET @OrderID =10249
SET @ProductID =NULL
SET @DyWhere =' WHERE'

SET @DyQuery ='SELECT [OrderID]
                                             ,[ProductID]
                                             ,[UnitPrice]
                                             ,[Quantity]
                                             ,[Discount]
                                              FROM [dbo].[OrderDetails]'


IF @OrderID IS NOT NULL
BEGIN
   SET @DyWhere =@DyWhere+ ' OrderID ='+CONVERT(nvarchar, @OrderID)
 
END

IF @ProductID IS NOT NULL
BEGIN
SET @DyWhere =@DyWhere + ' AND ProductID ='+CONVERT(nvarchar, @ProductID)
END

IF @OrderID IS NOT NULL OR @ProductID IS NOT NULL
BEGIN
SET @DyQuery =@DyQuery +@DyWhere
END


EXECUTE sp_ExecuteSQL @DyQuery

Find out more about  sp_ExecuteSQL

You can use above mentioned one of method according to your scenario , Last one (dynamic SQL query ) this can use for more dynamic scenarios.

Concatenating row values from table to single string using T-SQL

There are several ways to concatenate row values into a single string in SQL Server, including using custom SQL functions, COALESCE, or the FOR XML PATH clause. In this post, I will demonstrate how to perform string aggregation using XML PATH and COALESCE. To make these examples easy to follow, I'll be using the NORTHWND sample database to show these methods in action.

Example 1 : COALESCE (find more about COALESCE)

Using COALESCE function , we can concatenate many row values in to one single string. this is one use of COALESCE , there are many ,so you can find some more clicking above mention link.

Example 2: XML PATH

 1


2

To ensure our final string doesn't start with an extra comma, we use the STUFF function. STUFF works by deleting a specific portion of a string and replacing it with another. In this case, we use it to target the very first character—the extra comma—and replace it with nothing, effectively removing it from the beginning of our result.

Common Table Expression (CTE) in Sql Server

Common Table Expressions, or CTEs, can be thought of as temporary views that are created in memory for a single execution scope. They allow you to simplify complex joins and subqueries by defining a named result set that exists only until the next query runs. Whether you are using Recursive or Non-Recursive CTEs, understanding their limitations—such as being unindexable and requiring immediate execution—is key to writing efficient SQL code.

• We can take CTE as tempory view (can be thought as tempory result set) that create in memory

• Its scope valid until next query run

• CTE need to use just after it declaration  

• There are two type Recursive and Nonrecursive CTE

• Can define multiple CTE

• CTE are unindexable ( it cau use exist index in referenced object)

• CTE can't have constrain

• ORDER BY clause can't be used in the CTE_Query_Definition , execpt when use TOP keyword

Simple Example.

ex 1

WITH CTE_CUSTOMER_EX2
(         [CustomerID]
          ,[CompanyName]
  ,[ContactName]
  ,[ContactTitle]
  ,[Address]
  ,[City]
)
AS
(
SELECT [CustomerID]
  ,[CompanyName]
  ,[ContactName]
  ,[ContactTitle]
  ,[Address]
  ,[City]

  FROM .[dbo].[Customers]
)


SELECT * FROM CTE_CUSTOMER_EX2

ex 2

;WITH CTE_CUSTOMER_EX1
AS
(
SELECT [CustomerID]
 ,[CompanyName]
 ,[ContactName]
 FROM .[dbo].[Customers]

)
SELECT * FROM CTE_CUSTOMER_EX1

Note
If there are query before CTE define , need to use Semicolon teminator before declare CTE


Multiple CTE

  With CTE_M1 as 
(
-select statement
) 
     , CTE_M2 as 
(
-select statemet

)

you can find some more detail and examples using this Link and Link2