Comparison Functions and Operators

Comparison Operators

Range Operator: BETWEEN

The BETWEEN operator tests if a value is within a specified range. It uses the syntax value BETWEEN min AND max:

SELECT 3 BETWEEN 2 AND 6;

The statement shown above is equivalent to the following statement:

SELECT 3 >= 2 AND 3 <= 6;

To test if a value does not fall within the specified range use NOT BETWEEN:

SELECT 3 NOT BETWEEN 2 AND 6;

The statement shown above is equivalent to the following statement:

SELECT 3 < 2 OR 3 > 6;

A NULL in a BETWEEN or NOT BETWEEN statement is evaluated using the standard NULL evaluation rules applied to the equivalent expression above:

SELECT NULL BETWEEN 2 AND 4; -- null
SELECT 2 BETWEEN NULL AND 6; -- null
SELECT 2 BETWEEN 1 AND NULL; -- false
SELECT 8 BETWEEN NULL AND 6; -- false

The BETWEEN and NOT BETWEEN operators can also be used to evaluate any orderable type. For example, a VARCHAR:

SELECT 'Paul' BETWEEN 'John' AND 'Ringo'; -- true

Not that the value, min, and max parameters to BETWEEN and NOT BETWEEN must be the same type. For example, openLooKeng will produce an error if you ask it if John is between 2.3 and 35.2.

IS NULL and IS NOT NULL

The IS NULL and IS NOT NULL operators test whether a value is null (undefined). Both operators work for all data types.

Using NULL with IS NULL evaluates to true:

select NULL IS NULL; -- true

But any other constant does not:

SELECT 3.0 IS NULL; -- false

IS DISTINCT FROM and IS NOT DISTINCT FROM

In SQL a NULL value signifies an unknown value, so any comparison involving a NULL will produce NULL. The IS DISTINCT FROM and IS NOT DISTINCT FROM operators treat NULL as a known value and both operators guarantee either a true or false outcome even in the presence of NULL input:

SELECT NULL IS DISTINCT FROM NULL; -- false
SELECT NULL IS NOT DISTINCT FROM NULL; -- true

In the example shown above, a NULL value is not considered distinct from NULL. When you are comparing values which may include NULL use these operators to guarantee either a TRUE or FALSE result.

The following truth table demonstrate the handling of NULL in IS DISTINCT FROM and IS NOT DISTINCT FROM:

GREATEST and LEAST

These functions are not in the SQL standard, but are a common extension. Like most other functions in openLooKeng, they return null if any argument is null. Note that in some other databases, such as PostgreSQL, they only return null if all arguments are null.

The following types are supported: DOUBLE, BIGINT, VARCHAR, TIMESTAMP, TIMESTAMP WITH TIME ZONE, DATE

greatest(value1, value2, …, valueN) -> [same as input]

Returns the largest of the provided values.

least(value1, value2, …, valueN) -> [same as input]

Returns the smallest of the provided values.

Quantified Comparison Predicates: ALL, ANY and SOME

The ALL, ANY and SOME quantifiers can be used together with comparison operators in the following way:

expression operator quantifier ( subquery )

For example:

SELECT 'hello' = ANY (VALUES 'hello', 'world'); -- true
SELECT 21 < ALL (VALUES 19, 20, 21); -- false
SELECT 42 >= SOME (SELECT 41 UNION ALL SELECT 42 UNION ALL SELECT 43); -- true

Here are the meanings of some quantifier and comparison operator combinations: