TRUNCATE TABLE
Syntax
TRUNCATE [TABLE] tbl_name [WAIT n | NOWAIT]
Contents
Description
TRUNCATE TABLE
empties a table completely. It requires the DROP
privilege. See GRANT
.
tbl_name
can also be specified in the form db_name
.tbl_name
(see Identifier Qualifiers).
Logically, TRUNCATE TABLE
is equivalent to a DELETE
statement that deletes all rows, but there are practical differences under some circumstances.
TRUNCATE TABLE
is faster than DELETE
, because it drops and re-creates a table. With XtraDB/InnoDB, this is faster if the innodb_file_per_table variable is ON (the default since MariaDB 5.5).
TRUNCATE TABLE
will fail for an InnoDB table if any FOREIGN KEY constraints from other tables reference the table, returning the error:
ERROR 1701 (42000): Cannot truncate a table referenced in a foreign key constraint
Foreign Key constraints between columns in the same table are permitted.
For an InnoDB table, if there are no 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 by TRUNCATE TABLE
, regardless of whether there is a FOREIGN KEY
constraint.
The count of rows affected by TRUNCATE TABLE
is accurate only
when it is mapped to a DELETE
statement.
For other storage engines, TRUNCATE TABLE
differs from
DELETE
in the following ways:
- 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
tbl_name.frm
is valid, the table can be re-created as an empty table withTRUNCATE 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 MyISAM and InnoDB, which 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. - Since truncation of a table does not make any use of
DELETE
, theTRUNCATE
statement does not invokeON DELETE
triggers. TRUNCATE TABLE
will only reset the values in the Performance Schema summary tables to zero or null, and will not remove the rows.
For the purposes of binary logging and replication, TRUNCATE TABLE
is treated as DROP TABLE
followed by CREATE TABLE
(DDL rather than DML).
TRUNCATE TABLE
does not work on views.