MySQL 8.0 Reference Manual Including MySQL NDB Cluster 8.0

13.1.37 TRUNCATE TABLE Statement


TRUNCATE TABLE empties a table completely. It requires the DROP privilege. Logically, TRUNCATE TABLE is similar to a DELETE statement that deletes all rows, or a sequence of DROP TABLE and CREATE TABLE statements.

To achieve high performance, TRUNCATE TABLE bypasses the DML method of deleting data. Thus, it does not cause ON DELETE triggers to fire, it cannot be performed for InnoDB tables with parent-child foreign key relationships, and it cannot be rolled back like a DML operation. However, TRUNCATE TABLE operations on tables that use an atomic DDL-supported storage engine are either fully committed or rolled back if the server halts during their operation. For more information, see Section 13.1.1, “Atomic Data Definition Statement Support”.

Although TRUNCATE TABLE is similar to DELETE, it is classified as a DDL statement rather than a DML statement. It differs from DELETE in the following ways:

TRUNCATE TABLE is treated for purposes of binary logging and replication as DDL rather than DML, and is always logged as a statement.

TRUNCATE TABLE for a table closes all handlers for the table that were opened with HANDLER OPEN.

In MySQL 5.7 and earlier, on a system with a large buffer pool and innodb_adaptive_hash_index enabled, a TRUNCATE TABLE operation could cause a temporary drop in system performance due to an LRU scan that occurred when removing the table's adaptive hash index entries (Bug #68184). The remapping of TRUNCATE TABLE to DROP TABLE and CREATE TABLE in MySQL 8.0 avoids the problematic LRU scan.

TRUNCATE TABLE can be used with Performance Schema summary tables, but the effect is to reset the summary columns to 0 or NULL, not to remove rows. See Section 27.12.20, “Performance Schema Summary Tables”.

Truncating an InnoDB table that resides in a file-per-table tablespace drops the existing tablespace and creates a new one. As of MySQL 8.0.21, if the tablespace was created with an earlier version and resides in an unknown directory, InnoDB creates the new tablespace in the default location and writes the following warning to the error log: The DATA DIRECTORY location must be in a known directory. The DATA DIRECTORY location will be ignored and the file will be put into the default datadir location. Known directories are those defined by the datadir, innodb_data_home_dir, and innodb_directories variables. To have TRUNCATE TABLE create the tablespace in its current location, add the directory to the innodb_directories setting before running TRUNCATE TABLE.