Subquery operators¶

A subquery is a query within another query. Subquery operators perform operations on the values produced by subqueries.

Snowflake supports the following subquery operators:

ALL / ANY¶

The ALL and ANY keywords can be used to apply a comparison operator to the values produced by a subquery (which can return more than one row).

<expr> comparisonOperator { ALL | ANY } ( <query> ) 

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Where:

comparisonOperator ::= { = | != | > | >= | < | <= } 

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The expression is compared with the operator for each value that the subquery returns:
- If ALL is specified, then the result is TRUE if every row of the subquery satisfies the condition; otherwise, it returns FALSE.
- If ANY is specified, then the result is TRUE if any row of the subquery satisfies the condition; otherwise, it returns FALSE.
ANY/ALL subqueries are currently supported only in a WHERE clause.
ANY/ALL subqueries can’t appear as an argument to an OR operator.
The subquery must contain only one item in its SELECT list.

Use a != ALL subquery to find the departments that have no employees:

SELECT department_id FROM departments d WHERE d.department_id != ALL ( SELECT e.department_id FROM employees e); 

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An EXISTS subquery is a Boolean expression that can appear in a WHERE or HAVING clause, or in any function that operates on a Boolean expression:

An EXISTS expression evaluates to TRUE if any rows are produced by the subquery.
A NOT EXISTS expression evaluates to TRUE if no rows are produced by the subquery.

[ NOT ] EXISTS ( <query> ) 

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Correlated EXISTS subqueries are currently supported only in a WHERE clause.
Correlated EXISTS subqueries cannot appear as an argument to an OR operator.
Uncorrelated EXISTS subqueries are supported anywhere that a Boolean expression is allowed.

Use a correlated NOT EXISTS subquery to find the departments that have no employees:

SELECT department_id FROM departments d WHERE NOT EXISTS ( SELECT 1 FROM employees e WHERE e.department_id = d.department_id); 

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The IN and NOT IN operators check whether an expression is included in the values produced by a subquery.

<expr> [ NOT ] IN ( <query> ) 

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IN is shorthand for = ANY, and is subject to the same restrictions as ANY subqueries.
NOT IN is shorthand for != ALL, and is subject to the same restrictions as ALL subqueries.
[NOT] IN can also be used as an operator in expressions that don’t involve a subquery. For details, see [ NOT ] IN.

Use a NOT IN subquery that is equivalent to the != ALL subquery example (earlier in this topic) to find the departments that have no employees:

SELECT department_id FROM departments d WHERE d.department_id NOT IN ( SELECT e.department_id FROM employees e); 

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