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ESQL logical operators
The logical operators AND, OR and NOT.
ESQL provides the following logical operators:
- Operator AND
- The result is the logical AND of the two operands. Both operands must be Boolean values.
- Operator OR
- The result is the logical OR of the two operands. Both operands must be Boolean values.
- Operator NOT
- The result is the logical NOT of the operand, which must be a Boolean value.
NULL and UNKNOWN values are treated as special values by these operators, according to the following rules:
- NULL and UNKNOWN are treated the same.
- If an operand is NULL, the result is NULL unless the operation result is already dictated by the other parameter.
The evaluation of the individual clauses in a statement that includes the AND or OR logical
operators is stopped as soon as the overall statement can be resolved. For example, see the
following statements:
IF A OR B THEN ...
- If A is false, B is evaluated.
- If A is true, B is not evaluated because the statement is already resolved to be true.
IF A AND B THEN ...
- If A is true, B is evaluated.
- If A is false, B is not evaluated because the statement is already resolved to be false.
The result of AND and OR operations is defined by the following table:
Value of P | Value of Q | Result of P AND Q | Result of P OR Q |
---|---|---|---|
TRUE | TRUE | TRUE | TRUE |
TRUE | FALSE | FALSE | TRUE |
TRUE | UNKNOWN | UNKNOWN | TRUE |
FALSE | TRUE | FALSE | TRUE |
FALSE | FALSE | FALSE | FALSE |
FALSE | UNKNOWN | FALSE | UNKNOWN |
UNKNOWN | TRUE | UNKNOWN | TRUE |
UNKNOWN | FALSE | FALSE | UNKNOWN |
UNKNOWN | UNKNOWN | UNKNOWN | UNKNOWN |
The result of NOT operations is defined by the following table.
Operand | Result of NOT |
---|---|
TRUE | FALSE |
FALSE | TRUE |
UNKNOWN | UNKNOWN |