ASA SQL User's Guide
Using Subqueries
You can use the subquery set membership test to compare a value from the main query to more than one value in the subquery.
The subquery set membership test compares a single data value for each row in the main query to the single column of data values produced by the subquery. If the data value from the main query matches one of the data values in the column, the subquery returns TRUE.
Select the names of the employees who head the Shipping or Finance departments:
SELECT emp_fname, emp_lname FROM employee WHERE emp_id IN ( SELECT dept_head_id FROM department WHERE (dept_name='Finance' or dept_name = 'Shipping'))
emp_fname | emp_lname |
---|---|
Jose | Martinez |
Mary Anne | Shea |
The subquery in this example
SELECT dept_head_id FROM department WHERE (dept_name='Finance' OR dept_name = 'Shipping')
extracts from the department table the id numbers that correspond to the heads of the Shipping and Finance departments. The main query then returns the names of the employees whose id numbers match one of the two found by the subquery.
The subquery set membership test is equivalent to the =ANY test. The following query is equivalent to the query from the above example.
SELECT emp_fname, emp_lname FROM employee WHERE emp_id =ANY ( SELECT dept_head_id FROM department WHERE (dept_name='Finance' or dept_name = 'Shipping'))
You can also use the subquery set membership test to extract those rows whose column values are not equal to any of those produced by a subquery. To negate a set membership test, insert the word NOT in front of the keyword IN.
The subquery in this query returns the first and last names of the employees that are not heads of the Finance or Shipping departments.
SELECT emp_fname, emp_lname FROM employee WHERE emp_id NOT IN ( SELECT dept_head_id FROM department WHERE (dept_name='Finance' OR dept_name = 'Shipping'))