ClickHouse/docs/en/operations/settings/permissions-for-queries.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

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---
toc_priority: 58
toc_title: Permissions for Queries
---
# Permissions for Queries {#permissions_for_queries}
Queries in ClickHouse can be divided into several types:
1. Read data queries: `SELECT`, `SHOW`, `DESCRIBE`, `EXISTS`.
2. Write data queries: `INSERT`, `OPTIMIZE`.
3. Change settings query: `SET`, `USE`.
4. [DDL](https://en.wikipedia.org/wiki/Data_definition_language) queries: `CREATE`, `ALTER`, `RENAME`, `ATTACH`, `DETACH`, `DROP` `TRUNCATE`.
5. `KILL QUERY`.
The following settings regulate user permissions by the type of query:
- [readonly](#settings_readonly) — Restricts permissions for all types of queries except DDL queries.
- [allow\_ddl](#settings_allow_ddl) — Restricts permissions for DDL queries.
`KILL QUERY` can be performed with any settings.
## readonly {#settings_readonly}
Restricts permissions for reading data, write data and change settings queries.
See how the queries are divided into types [above](#permissions_for_queries).
Possible values:
- 0 — All queries are allowed.
- 1 — Only read data queries are allowed.
- 2 — Read data and change settings queries are allowed.
After setting `readonly = 1`, the user cant change `readonly` and `allow_ddl` settings in the current session.
When using the `GET` method in the [HTTP interface](../../interfaces/http.md), `readonly = 1` is set automatically. To modify data, use the `POST` method.
Setting `readonly = 1` prohibit the user from changing all the settings. There is a way to prohibit the user
from changing only specific settings, for details see [constraints on settings](../../operations/settings/constraints-on-settings.md).
Default value: 0
## allow\_ddl {#settings_allow_ddl}
Allows or denies [DDL](https://en.wikipedia.org/wiki/Data_definition_language) queries.
See how the queries are divided into types [above](#permissions_for_queries).
Possible values:
- 0 — DDL queries are not allowed.
- 1 — DDL queries are allowed.
You cant execute `SET allow_ddl = 1` if `allow_ddl = 0` for the current session.
Default value: 1
[Original article](https://clickhouse.tech/docs/en/operations/settings/permissions_for_queries/) <!--hide-->