Comparison functions and operators#

Примечание

Ниже приведена оригинальная документация Trino. Скоро мы ее переведем на русский язык и дополним полезными примерами.

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;

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

Note that the value, min, and max parameters to BETWEEN and NOT BETWEEN must be the same type. For example, Trino 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 Trino, 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.

Pattern comparison: LIKE#

The LIKE operator can be used to compare values with a pattern:

... column [NOT] LIKE 'pattern' ESCAPE 'character';

Matching characters is case sensitive, and the pattern supports two symbols for matching:

_ matches any single character
% matches zero or more characters

Typically it is often used as a condition in WHERE statements. An example is a query to find all continents starting with E, which returns Europe:

SELECT * FROM (VALUES 'America', 'Asia', 'Africa', 'Europe', 'Australia', 'Antarctica') AS t (continent)
WHERE continent LIKE 'E%';

You can negate the result by adding NOT, and get all other continents, all not starting with E:

SELECT * FROM (VALUES 'America', 'Asia', 'Africa', 'Europe', 'Australia', 'Antarctica') AS t (continent)
WHERE continent NOT LIKE 'E%';

If you only have one specific character to match, you can use the _ symbol for each character. The following query uses two underscores and produces only Asia as result:

SELECT * FROM (VALUES 'America', 'Asia', 'Africa', 'Europe', 'Australia', 'Antarctica') AS t (continent)
WHERE continent LIKE 'A__A';

The wildcard characters _ and % must be escaped to allow you to match them as literals. This can be achieved by specifying the ESCAPE character to use:

SELECT 'South_America' LIKE 'South\_America' ESCAPE '\';

The above query returns true since the escaped underscore symbol matches. If you need to match the used escape character as well, you can escape it.

If you want to match for the chosen escape character, you simply escape itself. For example, you can use \\ to match for „“'“.