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ClickHouse/docs/en/sql-reference/statements/select/where.md
Ivan Blinkov aa17da6b68
[docs] adjust SELECT ToC meta (#10942) 
* [docs] adjust SELECT ToC meta

* Update array-join.md

* Update distinct.md

* Update format.md

* Update from.md

* Update group-by.md

* Update having.md

* Update into-outfile.md

* Update join.md

* Update limit-by.md

* Update limit.md

* Update order-by.md

* Update prewhere.md

* Update sample.md

* Update union-all.md

* Update where.md

* Update with.md
2020-05-15 14:25:18 +03:00

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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.