2.0 KiB
| toc_priority | toc_title |
|---|---|
| 40 | ATTACH |
ATTACH Statement
Attaches the table, 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 to the server. After executing an ATTACH query, the server will know about the existence of the table.
If the table was previously detached (DETACH) query, meaning that its structure is known, you can use shorthand without defining the structure.
Syntax Forms
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.
Сreate New Table And Attach Data
With specify path to table data
ATTACH TABLE name FROM 'path/to/data/' (col1 Type1, ...)
It creates new table with provided structure and attaches table data from provided directory in user_files.
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 specify table UUID (Only for Atomic database)
ATTACH TABLE name UUID '<uuid>' (col1 Type1, ...)
It creates new table with provided structure and attaches data from table with the specified UUID.