Oracle PL/SQL for DBAs

Applying Criteria

When applying criteria to a function, be cognizant of performance, especially when deciding whether to pass parameter values into the function for use when assembling the result set or applying them to the returned result set. Here are two examples of what I mean. The first applies the criterion (col1 = ‘A') to returned records after they are assembled by the function.

    SELECT *
      FROM TABLE(a_function)
     WHERE col1 = 'A';

This next example passes the criterion directly into the function so it can be used when assembling records.

    SELECT *
      FROM TABLE(a_function('A');

Examine the complexity of the algorithm and the size of the data set to determine which approach will work best for you.