>>I've discovered numerous SPs, in the system I inherited, that rely on implicit conversion of parameters.
>>
>>I've read that it is a best practice to explicitly convert these parameters, but I would like to know if there is a performance gain using explicit conversion.
>>
>>Thanks.
>
>I really didn't test it, but for me if SQL Server should do some implicit conversion that will slow the query (with 0.000000(0)1 millisecond, just because that conversion is done once when the query is compiled.
>BUT to relay on implicit conversion is not good for me. What if you pass illegal parameter?
>Check this:
>

>DECLARE @test varchar(20)
>SET @Test = '0'
>
>SELECT 1 + @Test
>
>SET @Test = '0.0'
>SELECT 1 + @Test --BOOOOOOM
>


Thanks Borislav,

Those were my thoughts too.  I was just trying to decide if I should go through all 600+ SPs looking for implicit conversions, or fix them as I encounter them.  I think I'll just fix them when I run into them.