Implementing search functionality with multiple optional parameters against database table

Question

I would like to check if there is a preferred design pattern for implementing search functionality with multiple optional parameters against database table where the access

Answer 1

I posted this as a comment, but I realized it should probably be an answer.

It's not good to write predicates as WHERE @Param IS NULL OR Column = @Param, because the optimizer usually considers it to be non-sargable.

Try this experiment: Take your most populated table, and try to query just for the Primary Key field, which should be your clustered index:

DECLARE @PrimaryKey int
SET @PrimaryKey = 1

SELECT CoveredColumn
FROM Table
WHERE @PrimaryKey IS NULL
OR PrimaryKeyColumn = @PrimaryKey

SELECT CoveredColumn
FROM Table
WHERE PrimaryKeyColumn >= ISNULL(@PrimaryKey, 0)
AND PrimaryKeyColumn <= ISNULL(@PrimaryKey, 2147483647)

Both of these SELECT statements will produce identical results, assuming that the PK column is a non-negative int. But pull up the execution plan for this and you'll see a huge difference in cost. The first SELECT does a full index scan and typically takes up about 90% of the query cost.

When you want to have optional search conditions in SQL, and you can't use dynamic SQL, it's best for performance if you can turn it into a range query instead using ISNULL. Even if the range is huge (literally half the range of an int here), the optimizer will still figure it out when the optional parameter is used.