8.2. Comparison Functions and Operators

8.2. Comparison Functions and Operators

Comparison Operators

Operator	Description
`<`	Less than
`>`	Greater than
`<=`	Less than or equal to
`>=`	Greater than or equal to
`=`	Equal
`<>`	Not equal
`!=`	Not equal (non-standard but popular syntax)

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;

The presence of NULL in a BETWEEN or NOT BETWEEN statement will result in the statement evaluating to NULL:

SELECT NULL BETWEEN 2 AND 4; -- null
SELECT 2 BETWEEN NULL AND 6; -- null

The BETWEEN and NOT BETWEEN operators can also be used to evaluate string arguments:

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, Presto 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:

a	b	a = b	a <> b	a DISTINCT b	a NOT DISTINCT b
`1`	`1`	`TRUE`	`FALSE`	`FALSE`	`TRUE`
`1`	`2`	`FALSE`	`TRUE`	`TRUE`	`FALSE`
`1`	`NULL`	`NULL`	`NULL`	`TRUE`	`FALSE`
`NULL`	`NULL`	`NULL`	`NULL`	`FALSE`	`TRUE`

GREATEST and LEAST

These functions are not in the SQL standard, but are a common extension. Like most other functions in Presto, 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:

Expression	Meaning
`A = ALL (…)`	Evaluates to `true` when `A` is equal to all values.
`A <> ALL (…)`	Evaluates to `true` when `A` doesn’t match any value.
`A < ALL (…)`	Evaluates to `true` when `A` is smaller than the smallest value.
`A = ANY (…)`	Evaluates to `true` when `A` is equal to any of the values. This form is equivalent to `A IN (…)`.
`A <> ANY (…)`	Evaluates to `true` when `A` doesn’t match one or more values.
`A < ANY (…)`	Evaluates to `true` when `A` is smaller than the biggest value.

ANY and SOME have the same meaning and can be used interchangeably.

LIKE

The LIKE operator is used to match a specified character pattern in a string. Patterns can contain regular characters as well as wildcards. Wildcard characters can be escaped using the single character specified for the ESCAPE parameter. Matching is case sensitive.

Syntax:

expression LIKE pattern [ ESCAPE 'escape_character' ]

if pattern or escape_character is null, the expression evaluates to null.

Wildcard	Representation
`%`	The percent sign represents zero, one, or multiple characters
`_`	The underscore represents a single character

Examples:

SELECT * FROM (VALUES ('abc'), ('bcd'), ('cde')) AS t (name)
WHERE name LIKE '%b%'
--returns 'abc' and  'bcd'
SELECT * FROM (VALUES ('abc'), ('bcd'), ('cde')) AS t (name)
WHERE name LIKE '_b%'
--returns 'abc'
SELECT * FROM (VALUES ('abc'), ('bcd'), ('cde')) AS t (name)
WHERE name LIKE 'b%'
--returns 'bcd'
SELECT * FROM (VALUES ('abc'), ('bcd'), ('cde')) AS t (name)
WHERE name LIKE 'B%'
--returns nothing
SELECT * FROM (VALUES ('a_c'), ('_cd'), ('cde')) AS t (name)
WHERE name LIKE '%#_%' ESCAPE '#'
--returns 'a_c' and  '_cd'
SELECT * FROM (VALUES ('a%c'), ('%cd'), ('cde')) AS t (name)
WHERE name LIKE '%#%%' ESCAPE '#'
--returns 'a%c' and  '%cd'