Logical Conditions

A logical condition combines the results of two component conditions to produce a single result based on them or to invert the result of a single condition. Table 6-4 lists logical conditions.

Table 4 Logical Conditions

Type of Condition	Operation	Examples
NOT	Returns `TRUE` if the following condition is `FALSE`. Returns `FALSE` if it is `TRUE`. If it is `UNKNOWN`, then it remains `UNKNOWN`.	SELECT * FROM employees WHERE NOT (job_id IS NULL) ORDER BY employee_id; SELECT * FROM employees WHERE NOT (salary BETWEEN 1000 AND 2000) ORDER BY employee_id;
AND	Returns `TRUE` if both component conditions are `TRUE`. Returns `FALSE` if either is `FALSE`. Otherwise returns `UNKNOWN`.	SELECT * FROM employees WHERE job_id = 'PU_CLERK' AND department_id = 30 ORDER BY employee_id;
OR	Returns `TRUE` if either component condition is `TRUE`. Returns `FALSE` if both are `FALSE`. Otherwise returns `UNKNOWN`.	SELECT * FROM employees WHERE job_id = 'PU_CLERK' OR department_id = 10 ORDER BY employee_id;

Table 6-5 shows the result of applying the NOT condition to an expression.

Table 5 NOT Truth Table

–	TRUE	FALSE	UNKNOWN
`NOT`	`FALSE`	`TRUE`	`UNKNOWN`

Table 6-6 shows the results of combining the AND condition to two expressions.

Table 6 AND Truth Table

AND	TRUE	FALSE	UNKNOWN
`TRUE`	`TRUE`	`FALSE`	`UNKNOWN`
`FALSE`	`FALSE`	`FALSE`	`FALSE`
`UNKNOWN`	`UNKNOWN`	`FALSE`	`UNKNOWN`

For example, in the WHERE clause of the following SELECT statement, the AND logical condition is used to ensure that only those hired before 2004 and earning more than $2500 a month are returned:

SELECT * FROM employees
WHERE hire_date < TO_DATE('01-JAN-2004', 'DD-MON-YYYY')
  AND salary > 2500
  ORDER BY employee_id;

Table 6-7 shows the results of applying OR to two expressions.

Table 7 OR Truth Table

OR	TRUE	FALSE	UNKNOWN
`TRUE`	`TRUE`	`TRUE`	`TRUE`
`FALSE`	`TRUE`	`FALSE`	`UNKNOWN`
`UNKNOWN`	`TRUE`	`UNKNOWN`	`UNKNOWN`

For example, the following query returns employees who have a 40% commission rate or a salary greater than $20,000:

SELECT employee_id FROM employees
   WHERE commission_pct = .4 OR salary > 20000
   ORDER BY employee_id;