Predefined Variables for Expressions

In addition to using column names, literals, operators, and functions in an expression, you can use predefined variables that have defined meanings or values. For example, you can use a predefined variable to display the user name for the current user or to search for data columns that contain no value (null).

The list below includes examples of predefined variables.

Predefined Variable Description Example

Predefined Variable	Description	Example
CURRENT_USER	The user name of the current user	`UPDATE accounts SET salesperson = CURRENT_USER WHERE region = 'NW'` Changes the `salesperson` column for all accounts in the northwest region to the name of the current user.
NULL	A null value, used in the search expressions IS NULL and IS NOT NULL	`SELECT emp_id, lname, fname, minit FROM employee WHERE minit IS NULL` Finds authors who have no middle initial. Note The keyword IS is a special operator for use with NULL.

CURRENT_USER

The user name of the current user

UPDATE accounts 
SET salesperson = CURRENT_USER
WHERE region = 'NW'

Changes the salesperson column for all accounts in the northwest region to the name of the current user.

NULL

A null value, used in the search expressions
IS NULL and
IS NOT NULL

SELECT emp_id, lname, fname, minit
FROM employee
WHERE minit IS NULL

Finds authors who have no middle initial.

Note The keyword IS is a special operator for use with NULL.