7. IN & NOT IN keywords in SQL

SELECT col1, SUM(col2)

FROM "list-of-tables"

WHERE col3 IN (list-of-values);

The IN conditional operator is really a set membership test operator. That is, it is used to test whether or not a value (stated before the keyword IN) is "in" the list of values provided after the keyword IN.

For example:

SELECT employeeid, lastname, salary

FROM employee_info

WHERE lastname IN ('Hernandez', 'Jones', 'Roberts', 'Ruiz');

This statement will select the employeeid, lastname, salary from the employee_info table where the lastname is equal to either: Hernandez, Jones, Roberts, or Ruiz. It will return the rows if it is ANY of these values.

The IN conditional operator can be rewritten by using compound conditions using the equals operator and combining it with OR - with exact same output results:

SELECT employeeid, lastname, salary

FROM employee_info

WHERE lastname = 'Hernandez' OR lastname = 'Jones' OR lastname = 'Roberts'
OR lastname = 'Ruiz';

As you can see, the IN operator is much shorter and easier to read when you are testing for more than two or three values.

You can also use NOT IN to exclude the rows in your list.