TRUNCATE TABLE by
deleting rows one by one if there are any
KEY constraints that reference the table. If there are
FOREIGN KEY constraints,
InnoDB performs fast truncation by dropping the
original table and creating an empty one with the same definition,
which is much faster than deleting rows one by one. The
AUTO_INCREMENT counter is reset to zero by
TRUNCATE TABLE, regardless of
whether there is a
FOREIGN KEY constraint.
In the case that
FOREIGN KEY constraints
reference the table,
InnoDB deletes rows one by
one and processes the constraints on each one. If the
FOREIGN KEY constraint specifies
DELETE CASCADE, rows from the child
(referenced) table are deleted, and the truncated table becomes
empty. If the
FOREIGN KEY constraint does
TRUNCATE TABLE statement deletes
rows one by one and stops if it encounters a parent row that is
referenced by the child, returning this error:
ERROR 1451 (23000): Cannot delete or update a parent row: a foreign key constraint fails (`test`.`child`, CONSTRAINT `child_ibfk_1` FOREIGN KEY (`parent_id`) REFERENCES `parent` (`id`))
This is the same as a
statement with no
Truncate operations drop and re-create the table, which is much faster than deleting rows one by one, particularly for large tables.
Truncate operations cause an implicit commit.
Truncation operations cannot be performed if the session holds an active table lock.
Truncation operations do not return a meaningful value for the number of deleted rows. The usual result is “0 rows affected,” which should be interpreted as “no information.”
As long as the table format file
is valid, the table can be re-created as an empty table with
TRUNCATE TABLE, even if the
data or index files have become corrupted.
The table handler does not remember the last used
AUTO_INCREMENT value, but starts counting
from the beginning. This is true even for
normally do not reuse sequence values.
When used with partitioned tables,
TRUNCATE TABLE preserves the
partitioning; that is, the data and index files are dropped
and re-created, while the partition definitions
.par) file is unaffected.
TRUNCATE TABLE is treated for
purposes of binary logging and replication as
DROP TABLE followed by
CREATE TABLE — that is, as
DDL rather than DML. This is due to the fact that, when using
InnoDB and other transactional
storage engines where the transaction isolation level does not
allow for statement-based logging (
READ UNCOMMITTED), the
statement was not logged and replicated when using
mode. (Bug#36763) However, it is still applied on replication
InnoDB in the manner