ClickHouse any Function

The any function in ClickHouse is an aggregation function that returns an arbitrary value from the set of input values. It's commonly used when you need to select a representative value from a group, but don't care which specific value is chosen.

Syntax

any(column)

Official ClickHouse Documentation on any function

Example Usage

SELECT 
    user_id,
    any(visit_date) AS sample_visit_date
FROM user_visits
GROUP BY user_id

This query will return one arbitrary visit date for each user.

Common Issues

• The any function doesn't guarantee consistent results across multiple query executions with the same data.
• It's not suitable when you need a specific value (like the first, last, or maximum).

Best Practices

• Use any when the specific value doesn't matter, but you need a representative from the group.
• Consider using anyLast if you want the last inserted value in the group.
• For deterministic results, use functions like min, max, or argMin/argMax instead.

Frequently Asked Questions

Q: What's the difference between any and anyLast in ClickHouse?
A: While any returns an arbitrary value from the group, anyLast returns the last value that was inserted into the group. anyLast is more deterministic but may be slightly slower.

Q: Can any be used with multiple columns?
A: Yes, you can use any with multiple columns independently. For example: SELECT any(col1), any(col2) FROM table GROUP BY group_col.

Q: Is the any function performant for large datasets?
A: Yes, any is generally very fast as it doesn't need to process all values in the group to determine the result.

Q: How does any handle NULL values?
A: any will return NULL if all values in the group are NULL. Otherwise, it will return a non-NULL value if one exists.

Q: Can any be used in a HAVING clause?
A: Yes, any can be used in a HAVING clause, but remember that the result may not be consistent across query executions.