T-SQL - How to write a conditional join

Question

I have a stored procedure with a number of parameters. I would like to write my query so that it joins with certain tables but only if a particular parameter has a value. Take

Answer 1

This is how I had done for my case.

DECLARE
    @ColorParam varchar(500)

SET
    @ColorParam = 'red, green, blue'

declare @Colors table
(
    Color NVARCHAR(50) PRIMARY KEY
)

-- populate @Colors table by parsing the input param, 
-- table can be empty if there is nothing to parse, i.e.: no condition
INSERT @Colors SELECT Value FROM dbo.Splitter(@ColorParam, ',')

SELECT
    m.Col1,
    c.Color
FROM
    MainTable AS m
FULL JOIN -- instead of using CROSS JOIN which won't work if @Colors is empty
    @Colors AS c
ON
    1 = 1 -- the trick
WHERE
    (@ColorParam IS NULL OR c.Color = m.Color)