database - SQL ignore part of WHERE if parameter is null

Question

I have a stored procedure that fetches info from a table based on 4 parameters.

I want to get values based on the parameters, but if a parameter is NULL then that parameter isn't checked. So if all 4 parameters is null I would show the entire table.

This is my SP (as you can see, this only works for 1 parameter atm):

CREATE PROCEDURE myProcedure
    @Param1 nvarchar(50),
    @Param2 nvarchar(50),
    @Param3 nvarchar(50),
    @Param4 nvarchar(50)
AS
BEGIN
    IF(@Param1 IS NULL)
        BEGIN
            SELECT Id, col1, col2, col3, col4 FROM myTable
        END
    ELSE
        BEGIN
            SELECT Id, col1, col2, col3, col4 FROM myTable WHERE col1 LIKE @Param1+'%'
        END
END

Is there some way to do this without having a IF for every possible combination (15 IFs)?

Answer 1

How about something like

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   col1 LIKE @Param1+'%'
OR      @Param1 IS NULL

in this specific case you could have also used

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   col1 LIKE ISNULL(@Param1,'')+'%'

But in general you can try something like

SELECT Id, col1, col2, col3, col4 
FROM    myTable 
WHERE   (condition1 OR @Param1 IS NULL)
AND     (condition2 OR @Param2 IS NULL)
AND     (condition3 OR @Param3 IS NULL)
...
AND     (conditionN OR @ParamN IS NULL)