thevar1able/ClickHouse
1
0
Fork 0
mirror of https://github.com/ClickHouse/ClickHouse.git synced 2024-11-21 23:21:59 +00:00
Code Issues Packages Projects Releases Wiki Activity

doc: Warn about MV using column names during insertion

Browse Source
This commit is contained in:
Thomas Berdy 2021-08-27 18:40:35 +02:00 committed by GitHub
parent 308fb6112d
commit e5511944bc
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 3 additions and 0 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

3
docs/en/sql-reference/statements/create/view.md
View File

@ -49,6 +49,9 @@ When creating a materialized view with `TO [db].[table]`, you must not use `POPU
A materialized view is implemented as follows: when inserting data to the table specified in `SELECT`, part of the inserted data is converted by this `SELECT` query, and the result is inserted in the view.
!!! important "Important"
Materialized views in ClickHouse use **column names** instead of column order during insertion into destination table. If some column names are not present in `SELECT`'s result ClickHouse will use a default value, even if column is not `Nullable`. A safe practice would be to add aliases for every column when using Materialized views.
!!! important "Important"
Materialized views in ClickHouse are implemented more like insert triggers. If there’s some aggregation in the view query, it’s applied only to the batch of freshly inserted data. Any changes to existing data of source table (like update, delete, drop partition, etc.) does not change the materialized view.