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