Question

I have two tables on which i have performed inner join. I have a scenario where i need to fetch values from the first table based on the two conditions.

My query is

SELECT rm.ROUTE_ID
            , rm.ROUTE_CODE
            , rm.START_PLACE_ID
            , rm.END_PLACE_ID
            , rm.IS_ACTIVE
            , rm.LINKED_ROUTE
        FROM OPRS_ROUTE_MASTER rm
        INNER JOIN OPRS_ROUTE_HALTS rh
            ON rh.ROUTE_ID = rm.ROUTE_ID
        WHERE rh.PLACE_ID  = '51'

now i need to have two more conditions in the where clause.

case 1: when rm.START_PLACE_ID > 0 then i need to append AND rm.START_PLACE_ID to where clause

case 2: when rm.END_PLACE_ID > 0 then i need to append AND rm.START_PLACE_ID to where clause

if both are greater than zero then i need to append both the cases to the where clause.

Can some one please help me

Answer 1

I’d set the query up something like this:

select rm.ROUTE_ID       ,
       rm.ROUTE_CODE     ,
       rm.START_PLACE_ID ,
       rm.END_PLACE_ID   ,
       rm.IS_ACTIVE      ,
       rm.LINKED_ROUTE
from OPRS_ROUTE_MASTER rm
join OPRS_ROUTE_HALTS  rh on rh.ROUTE_ID = rm.ROUTE_ID
                         and rh.PLACE_ID = '51'
where rm.START_PLACE_ID = case when rm.START_PLACE_ID > 0 then @myStartPlaceID else rm.START_PLACE_ID end
  and rm.END_PLACE_ID   = case when rm.END_PLACE_ID   > 0 then @myEndPlaceID   else rm.END_PLACE_ID   end

If the table row has a positive value in the desired column (START_PLACE_ID or END_PLACE_ID), the column is compared to the desired value, otherwise it’s compared to itself.

This avoids the use of alternation (the OR operator): using OR can degrade the execution plan, forcing a table or index scan rather than a seek.