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5. Expressions
6. Simple Expressions

# Simple Expressions

#### Logical Expressions

Logical Operators lists the operators and calculation rules of logical expressions.

#### Comparative Expressions

Comparison Operators lists the common comparative operators.

In addition to comparative operators, you can also use the following sentence structure:

• BETWEEN operator

a BETWEEN x AND y is equivalent to a >= x AND a <= y.

a NOT BETWEEN x AND y is equivalent to a < x OR a > y.

• To check whether a value is null, use:

expression IS NULL

expression IS NOT NULL

or an equivalent (non-standard) sentence structure:

expression ISNULL

expression NOTNULL Do not write expression=NULL or expression<>(!=)NULL, because NULL represents an unknown value, and these expressions cannot determine whether two unknown values are equal.

#### Examples

```SELECT 2 BETWEEN 1 AND 3 AS RESULT;
result
----------
t
(1 row)

SELECT 2 >= 1 AND 2 <= 3 AS RESULT;
result
----------
t
(1 row)

SELECT 2 NOT BETWEEN 1 AND 3 AS RESULT;
result
----------
f
(1 row)

SELECT 2 < 1 OR 2 > 3 AS RESULT;
result
----------
f
(1 row)

SELECT 2+2 IS NULL AS RESULT;
result
----------
f
(1 row)

SELECT 2+2 IS NOT NULL AS RESULT;
result
----------
t
(1 row)

SELECT 2+2 ISNULL AS RESULT;
result
----------
f
(1 row)

SELECT 2+2 NOTNULL AS RESULT;
result
----------
t
(1 row)

SELECT 2+2 IS DISTINCT FROM NULL AS RESULT;
result
----------
t
(1 row)

SELECT 2+2 IS NOT DISTINCT FROM NULL AS RESULT;
result
----------
f
(1 row)```