Conditional Expressions

This page covers conditional operators and functions in Rockset.

Operators

These operators are often useful in the WHERE clause of a SELECT statement.

Any operator that optionally includes NOT will return the opposite boolean when NOT is included.

Logical Operators

Rockset supports the basic logical operators shown below.

If any expression is null or undefined the result will be null.

Comparison Operators

Rockset supports the basic comparison operators shown below.

Expressions can be of any type. The result will be null if the two sides are different types, unless they are both numeric types.

BETWEEN

x [NOT] BETWEEN a AND b

This is equivalent to the expression below (without NOT).

x >= a

AND x <= b

CASE

CASE
    [expression]
    WHEN expr1 THEN value1
    [...]
    [ ELSE default_value ]
END

CASE is like an IF-THEN-ELSE statement. It executes a series of conditions and returns the value corresponding to the condition that evaluated to true.

It can have two behaviors:

• if expression is not given, expressions following WHEN are evaluated as boolean expressions.
• if expression is given, expressions following WHEN are checked for equality against expression.

The two queries below are equivalent and return the same results.

SELECT

    userEmail,

    CASE

        WHEN REGEXP_LIKE(userEmail, 'user1@') THEN 'User 1'

        WHEN REGEXP_LIKE(userEmail, 'user2@') THEN 'User 2'

        ELSE 'Unknown User'

    END AS username

FROM

    _events

LIMIT

    5

SELECT

    userEmail,

    CASE

        REGEXP_EXTRACT(userEmail, '(.*?)@', 1)

        WHEN 'user1' THEN 'User 1'

        WHEN 'user2' THEN 'User 2'

        ELSE 'Unknown User'

    END AS username

FROM

    _events

LIMIT

    5

+-------------------+--------------+
| userEmail         | username     |
|-------------------+--------------|
| user1@rockset.com | User 1       |
| user2@rockset.com | User 2       |
| user5@rockset.com | Unknown User |
| user1@rockset.com | User 1       |
| user2@rockset.com | User 2       |
+-------------------+--------------+

EXISTS

[NOT] EXISTS x

EXISTS evaluates to true if the specified subquery returns at least one row. If the subquery returns zero rows, it evaluates to false.

SELECT

    *

FROM

    customers c

WHERE

    EXISTS (

        SELECT

            1

        FROM

            payments p

        WHERE

            c.id = p.customer_id

            AND p.payment > 10000

    )

IN

x [NOT] IN y

The IN predicate determines if the expression x is equal to any values provided by y, which can be:

• A subquery, producing exactly one column, enclosed in parentheses
• A list of values, enclosed in parentheses () and separated by commas (such as (1, 'a')). An example of each form is shown below.
• See below for how this works using the WITH command

Note: The value for y cannot be an array. If y is an array, use the ARRAY_CONTAINS function.

SELECT

    *

FROM

    users

WHERE

    users.user_name IN (

        SELECT

            qualified_users.user_name

        FROM

            qualified_users

    )

SELECT

    *

FROM

    users

WHERE

    users.user_name IN ('admin', 'root')

WITH Statement: To use IN with the results of a WITH statement, wrap that statement in a subquery that fetches all rows. Instead of writing WITH cryptographers () ... WHERE x in cryptographers (which won't work), instead write where x in (SELECT y from cryptographers)

IS DISTINCT FROM

x IS [NOT] DISTINCT FROM y

Returns true if x is not equal to y, and false otherwise.

IS NULL

x IS [NOT] NULL

Returns true if x is null or undefined.

IS UNDEFINED

x IS [NOT] UNDEFINED

Returns true if x is undefined.

LIKE

x [NOT] LIKE y

Returns true if x and y (which must be of string or bytes type) match. A match is the same as equality, except also accounting for the following wildcard characters:

• % represents zero, one, or multiple characters.
• _ represents exactly one character.

SELECT

    'abc' LIKE 'ab'

false

SELECT

    'abc' LIKE 'ab_'

true

SELECT

    'abc' LIKE 'a_'

false

SELECT

    'abc' LIKE 'a%'

true

SELECT

    'abc' LIKE 'a_c'

true

TRY

TRY(expression)

Returns the result of evaluating expression. If an error is encountered while evaluating expression, returns null instead.

SELECT

    TRY(1 / 0)

null

SELECT

    TRY(CAST('foo' AS int))

null

SELECT

    TRY(CONCAT('rock', 'set'))

'rockset'

Functions

COALESCE

COALESCE(x, ...)

Returns the first non-null value in the argument list.

Note: undefined behaves the same as null in almost all functions, so it is ignored in COALESCE as well.

IF

IF(cond, x, y)

Returns x if cond is true, y otherwise.

NULLIF

NULLIF(value1, value2)

Returns null if value1 equals value2, otherwise returns value1.