Procedures with variable execution paths and optimization

Executing a stored procedure saves abstract plans for each statement that can be optimized, even if the stored procedure contains control-of-flow statements that can cause different statements to be run depending on parameters to the procedure or other conditions. If the query is run a second time with different parameters that use a different code path, plans for any statements that were optimized and saved by the earlier execution, and the abstract plan for the statement is associated with the query.

However, abstract plans for procedures do not solve the problem with procedures with statements that are optimized differently depending on conditions or parameters. One example is a procedure where users provide the low and high values for a between clause, with a query such as:

select title_id
from titles
where price between @lo and @hi

Depending on the parameters, the best plan could either be index access or a table scan. For these procedures, the abstract plan may specify either access method, depending on the parameters when the procedure was first executed. For more information on optimization of procedures, see “Splitting stored procedures to improve costing”.