2.4 KiB
| toc_priority | toc_title |
|---|---|
| 40 | ATTACH |
ATTACH Statement
Attaches a table or a dictionary, for example, when moving a database to another server.
Syntax
ATTACH TABLE|DICTIONARY [IF NOT EXISTS] [db.]name [ON CLUSTER cluster] ...
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
Syntax
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
The query creates a new table with provided structure and attaches table data from the provided directory in user_files.
Syntax
ATTACH TABLE name FROM 'path/to/data/' (col1 Type1, ...)
Example
Query:
DROP TABLE IF EXISTS test;
INSERT INTO TABLE FUNCTION file('01188_attach/test/data.TSV', 'TSV', 's String, n UInt8') VALUES ('test', 42);
ATTACH TABLE test FROM '01188_attach/test' (s String, n UInt8) ENGINE = File(TSV);
SELECT * FROM test;
Result:
┌─s────┬──n─┐
│ test │ 42 │
└──────┴────┘
With Specified Table UUID
This query creates a new table with provided structure and attaches data from the table with the specified UUID. It is supported by the Atomic database engine.
Syntax
ATTACH TABLE name UUID '<uuid>' (col1 Type1, ...)
Attach Existing Dictionary
Attaches a previously detached dictionary.
Syntax
ATTACH DICTIONARY [IF NOT EXISTS] [db.]name [ON CLUSTER cluster]