In my case it doesn't matter because I only select one particular Registration Record (RegID). So, I decided to save one parameter (if I would use two parameters, I would have to change several places to add the second parameter).

>>Hi everybody,
>>
>>I'm just wondering what would be better in your opinion:
>>

>>SELECT Registration.*, Schools.SchoolPhone
>>		FROM dbo.Registration LEFT JOIN Schools ON Registration.School = Schools.School
>>AND Schools.SiteID = @SiteID
>>        WHERE RegistrationID = @RegistrationID

>>
>>or
>>

>>SELECT Registration.*, Schools.SchoolPhone
>>		FROM dbo.Registration LEFT JOIN Schools ON Registration.School = Schools.School
>>AND Registration.SiteID = Schools.SiteID
>>        WHERE RegistrationID = @RegistrationID

>>
>>In other words, is it better to use parameter or field value? In the first case I would need to adjust several pages to add an extra parameter.
>>
>>Thanks a lot in advance.
>>
>>On the second thought - why do I care for one record return? LOL.
>
>It depends what you want. When you use variable and use it in JOIN you will filter joined table for only these records that match the variable. If you use Table Field in join you will filter matching fields no matter what value they have:
>

>Registration:
>SiteId    School
>-------------------------------
>1         1
>2         1
>3         1
>4         2
>5         2
>
>Schools:
>SiteId      School
>-------------------------------
>1            1
>2            1
>

>
>So this:
>

>SELECT *
>       FROM Registration
>LEFT JOIN Schools ON Registration.School = Schools.School AND
>          Registration.SiteId = Schools.SiteId
>

>
>will give you this:
>

>Schools:
>SiteId      School SiteId      School
>-------------------------------------
>1            1       1          1
>2            1       2          1
>3            1      NULL      NULL
>4            2      NULL      NULL
>5            2      NULL      NULL
>

>
>
>But:
>

>DECLARE @SiteId int
>SET @SiteId = 1
>SELECT *
>       FROM Registration
>LEFT JOIN Schools ON Registration.School = Schools.School AND
>          Schools.SiteId = @SiteId
>

>
>will give you this:
>

>Schools:
>SiteId      School SiteId      School
>-------------------------------------
>1            1       1          1
>2            1      NULL      NULL
>3            1      NULL      NULL
>4            2      NULL      NULL
>5            2      NULL      NULL
>