Boolean Value Expressions
Wed, 03/04/2009 - 20:02 | 
hdanzl
Specify a boolean value.
Syntax
|
| |
|
| |
<boolean term> AND <boolean factor> |
|
| | |
TRUE FALSE UNKNOWN |
|
| |
Notes
| ♦ | The declared type of a boolean primary shall be boolean. |
| ♦ | The AND and OR boolean operators are used to combine two or more predicates. |
| ♦ | The NOT operator inverts the meaning of a boolean expression. |
| ♦ | The boolean test: |
<boolean primary> IS NOT <truth value>
is equivalent to:
NOT <boolean primary> IS <truth value>
Since SQL supports null values and predicates whose value can be UNKNOWN, a three-valued logic is used to evaluate boolean value expressions. The rules of this logic are summarized in the following tables:
Truth Table for the AND Boolean Operator
|
AND |
True |
False |
Unknown |
|
True False Unknown |
True False Unknown |
False False False |
Unknown False Unknown |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
_____________________________________________________________________________
Truth Table for the OR Boolean Operator
|
OR |
True |
False |
Unknown |
|
True False Unknown |
True True True |
True False Unknown |
True Unknown Unknown |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
_____________________________________________________________________________
Truth Table for the NOT Boolean Operator
|
NOT |
|
|
True False Unknown |
False True Unknown |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
_____________________________________________________________________________
Truth Table for the IS Boolean Operator
|
IS |
True |
False |
Unknown |
|
True False Unknown |
True False False |
False True False |
False False True |
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
_____________________________________________________________________________
Examples
| 1) | The following example selects students from Newport, CA: |
SELECT studentID, studentName, city, state
FROM students
WHERE city = 'Newport' AND state = 'CA'
| 2) | The following example selects students from Newport, CA and RI: |
SELECT studentID, studentName, city, state
FROM students
WHERE city = 'Newport' AND ( state = 'CA' OR state = 'RI' )
| 3) | The following example selects students from Massachusetts and Newport, CA: |
SELECT studentID, studentName, city, state
FROM students
WHERE ( city = 'Newport' AND state = 'CA' ) OR state = 'MA'
| 4) | The following example selects all students except those from California and Boston, MA: |
SELECT studentID, studentName, city, state
FROM students
WHERE NOT ( ( city = 'Boston' AND state = 'MA' ) OR state = 'CA' )
Conformance
|
SQL:2003 standard |
- - |
Feature T031 "BOOLEAN data type" Feature F571 "Truth value tests" |
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