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# SQL As Understood By SQLite

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## ATTACH DATABASE

#### attach-stmt:

The ATTACH DATABASE statement adds another database file to the current database connection. The database-names 'main' and 'temp' refer to the main database and the database used for temporary tables. The main and temp databases cannot be attached or detached.

Tables in an attached database can be referred to using the syntax database-name.table-name. If the name of the table is unique across all attached databases and the main and temp databases, then the database-name prefix is not required. If two or more tables in different databases have the same name and the database-name prefix is not used on a table reference, then the table chosen is the one in the database that was least recently attached.

Transactions involving multiple attached databases are atomic, assuming that the main database is not ":memory:" and the journal_mode is not WAL. If the main database is ":memory:" or if the journal_mode is WAL, then transactions continue to be atomic within each individual database file. But if the host computer crashes in the middle of a COMMIT where two or more database files are updated, some of those files might get the changes where others might not.

There is is a limit, set using sqlite3_limit() and SQLITE_LIMIT_ATTACHED, to the number of databases that can be simultaneously attached to a single database connection.

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