thevar1able/ClickHouse
1
0
Fork 0
mirror of https://github.com/ClickHouse/ClickHouse.git synced 2024-11-14 11:33:46 +00:00
Code Issues Packages Projects Releases Wiki Activity
11039f1d17
ClickHouse/docs/en/sql-reference/statements/select/where.md
Ivan Blinkov 7170f3c534
[docs] split aggregate function and system table references (#11742) 
* prefer relative links from root

* wip

* split aggregate function reference

* split system tables
2020-06-18 11:24:31 +03:00

705 B
Raw Blame History

toc_title
WHERE

WHERE Clause

WHERE clause allows to filter the data that is coming from FROM clause of SELECT.

If there is a WHERE clause, it must contain an expression with the UInt8 type. This is usually an expression with comparison and logical operators. Rows where this expression evaluates to 0 are expluded from further transformations or result.

WHERE expression is evaluated on the ability to use indexes and partition pruning, if the underlying table engine supports that.

!!! note "Note" There’s a filtering optimization called prewhere.