Simple Expressions

Logical Expressions

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

Comparative Expressions

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

  NOTICE: 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

postgres=# SELECT 2 BETWEEN 1 AND 3 AS RESULT;
 result 
----------
 t
(1 row)

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

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

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

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

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

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

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

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

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