Syntax

TRUNCATE [TABLE] tbl_name
  [WAIT n | NOWAIT]

Description

TRUNCATE TABLE empties a table completely. It requires the DROP privilege (before 5.1.16, it required the DELETE 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.

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

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 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 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, the TRUNCATE statement does not invoke ON 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.

MariaDB starting with 10.3.0

WAIT/NOWAIT

Set the lock wait timeout. See WAIT and NOWAIT.

Comments

Comments loading...