SQL do inner join if condition met

Question

i want a good way to improve my sql code, i have to use inner join when condition is met. I am currently replicates the code:

@SystemMerge bit

if (@SystemMe         


        

Answer 1

This should (approxmately) do the same thing:

SELECT
     .......
  FROM myTable
  INNER JOIN table ON table.param1=myTable.param1
  LEFT JOIN systemTable on systemTable.param2=myTable.param2 and @SystemMerge = 1
  WHERE (@SystemMerge = 0 OR systemTable.NonNullableColumn IS NOT NULL)

Of course, this also means that any other references to columns within systemTable must be written to expect such columns to be NULL.