mirror of
https://github.com/ClickHouse/ClickHouse.git
synced 2024-11-13 19:14:30 +00:00
7170f3c534
* prefer relative links from root * wip * split aggregate function reference * split system tables
15 lines
705 B
Markdown
15 lines
705 B
Markdown
---
|
||
toc_title: WHERE
|
||
---
|
||
|
||
# WHERE Clause {#select-where}
|
||
|
||
`WHERE` clause allows to filter the data that is coming from [FROM](../../../sql-reference/statements/select/from.md) 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](../../../sql-reference/statements/select/prewhere.md).
|