SET PLANONLY
SET PLANONLY [ON | OFF]
This command prevents isql from actually executing the SQL statement, and instead only shows the plan that would be used to access the data.This command relies on the [isql-set-plan] command.If set plan off had been executed, this command would have no effect, so turning planonly on has the additional effect of executing set plan on implicitly.Executing set planonly off does not implicitly execute set plan off.
SQL> set planonly on; SQL> select count(*) from employee; PLAN (EMPLOYEE NATURAL)
As before, not supplying a parameter toggles the current setting.