ClickHouse ATTACH Statement

Attaches a table or a dictionary, for example, when moving a database to another server.

The query does not create data on the disk, but assumes that data is already in the appropriate places, and just adds information about the table or the dictionary to the server. After executing the ATTACH query, the server will know about the existence of the table or the dictionary.

If a table was previously detached (DETACH query), meaning that its structure is known, you can use shorthand without defining the structure.

Attach Existing Table​

ATTACH TABLE [IF NOT EXISTS] [db.]name [ON CLUSTER cluster]

This query is used when starting the server. The server stores table metadata as files with ATTACH queries, which it simply runs at launch (with the exception of some system tables, which are explicitly created on the server).

If the table was detached permanently, it won’t be reattached at the server start, so you need to use ATTACH query explicitly.

Create New Table And Attach Data

With Specified Path to Table Data

ATTACH TABLE name FROM 'path/to/data/' (col1 Type1, ...)

Example

DROP TABLE IF EXISTS test;
INSERT INTO TABLE FUNCTION file('0047_attach_data/test/data.TSV', 'TSV', 's String, n UInt8') VALUES ('test', 47);
ATTACH TABLE test FROM '0047_attach_data/test' (s String, n UInt8) ENGINE = File(TSV);
SELECT * FROM test;

Result;

┌─s────┬──n─┐
│ test │ 47 │
└──────┴────┘

With Specified Table UUID​

ATTACH TABLE name UUID '<uuid>' (col1 Type1, ...)

Attach Existing Dictionary​

Attaches a previously detached dictionary.

ATTACH DICTIONARY [IF NOT EXISTS] [db.]name [ON CLUSTER cluster]

To more information please visit officical ClickHouse docs in here.