December 2002
Intermediate to advanced
928 pages
85h 29m
English
Content preview from Oracle in a Nutshell
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Logical Conditions
A logical condition is a condition that can return one of three values—TRUE, FALSE, or UNKNOWN (which, in Oracle, is known as NULL). The three logical conditions supported by Oracle are NOT, AND, and OR.
The results of the NOT conditions for three-state logic (TRUE, FALSE, and UNKNOWN or NULL) are:
| NOT TRUE = FALSE |
| NOT FALSE = TRUE |
| NOT UNKNOWN = UNKNOWN (NULL) |
Table B-2 provides the results of comparisons with combinations of these conditions:
Table B-2. Combinations of logical conditions
|
Comparison |
Value |
TRUE |
FALSE |
UNKNOWN |
|---|---|---|---|---|
|
AND |
TRUE |
TRUE |
FALSE |
UNKNOWN |
|
FALSE |
FALSE |
FALSE |
FALSE | |
|
UNKNOWN |
UNKNOWN |
FALSE |
UNKNOWN | |
|
OR |
TRUE |
TRUE |
TRUE |
TRUE |
|
FALSE |
TRUE |
FALSE |
UNKNOWN | |
|
UNKNOWN |
TRUE |
UNKNOWN |
UNKNOWN |
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