ClickHouse/docs/en/system_tables/index.rst

System tables
==========

System tables are used for implementing part of the system's functionality, and for providing access to information about how the system is working.
You can't delete a system table (but you can perform DETACH).
System tables don't have files with data on the disk or files with metadata. The server creates all the system tables when it starts.
System tables are read-only.
System tables are located in the 'system' database.

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    :glob:

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