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ClickHouse/docs/en/sql-reference/table-functions/index.md
Smita Kulkarni 6a8fa2d4a5 Added new field allow_readonly in system.table_functions to allow using table functions in readonly mode. 
Implementation:
* Added a new field allow_readonly to table system.table_functions.
* Updated to use new field allow_readonly to allow using table functions in readonly mode.
* Added TableFunctionProperties similar to AggregateFunctionProperties.
* The functions allowed in readonly mode are in this set table_functions_allowed_in_readonly_mode.
Testing:
* Added a test for filesystem tests/queries/0_stateless/02473_functions_in_readonly_mode.sh
Documentation:
* Updated the english documentation for Table Functions.
2022-10-26 18:45:23 +02:00

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/en/sql-reference/table-functions/ Table Functions 34

Table Functions

Table functions are methods for constructing tables.

You can use table functions in:

  • FROM clause of the SELECT query.

    The method for creating a temporary table that is available only in the current query. The table is deleted when the query finishes.

  • CREATE TABLE AS table_function() query.

It's one of the methods of creating a table.

:::warning You can’t use table functions if the allow_ddl setting is disabled. :::

Function Description
file Creates a File-engine table.
merge Creates a Merge-engine table.
numbers Creates a table with a single column filled with integer numbers.
remote Allows you to access remote servers without creating a Distributed-engine table.
url Creates a Url-engine table.
mysql Creates a MySQL-engine table.
postgresql Creates a PostgreSQL-engine table.
jdbc Creates a JDBC-engine table.
odbc Creates a ODBC-engine table.
hdfs Creates a HDFS-engine table.
s3 Creates a S3-engine table.
sqlite Creates a sqlite-engine table.

:::note Only these table functions are enabled in readonly mode : null, view, viewIfPermitted, numbers, numbers_mt, generateRandom, values, cluster, clusterAllReplicas :::