Data Manipulation Language
A data manipulation language (DML) is a computer programming language used for adding (inserting), deleting, and modifying (updating) data in a database. A DML is often a sublanguage of a broader database language such as SQL, with the DML com ...
(DML) operation that deletes all rows of a table without causing a triggered action. The result of this operation quickly removes all data from a
table
Table may refer to:
* Table (furniture), a piece of furniture with a flat surface and one or more legs
* Table (landform), a flat area of land
* Table (information), a data arrangement with rows and columns
* Table (database), how the table data ...
, typically bypassing a number of integrity enforcing mechanisms. It was officially introduced in the SQL:2008 standard, as the optional feature F200, "TRUNCATE TABLE statement".
TRUNCATE TABLE removes all rows from a table, but the table structure and its columns, constraints, indexes, and so on remain. To remove the table definition in addition to its data, use the DROP TABLE statement.
The TRUNCATE TABLE mytable statement is logically (though not physically) equivalent to the DELETE FROM mytable statement (without a
WHERE
Where may refer to:
* Where?, one of the Five Ws in journalism
* where (command), a shell command
* Where (SQL), a database language clause
* Where.com, a provider of location-based applications via mobile phones
* ''Where'' (magazine), a serie ...
clause). The following characteristics distinguish TRUNCATE TABLE from DELETE:
* In the Oracle Database, TRUNCATE is implicitly preceded and followed by a commit operation. (This may also be the case in
MySQL
MySQL () is an open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A relational database ...
, when using a transactional storage engine.)
* Typically, TRUNCATE TABLE quickly deletes all records in a table by deallocating the data pages used by the table. This reduces the resource overhead of logging the deletions, as well as the number of
locks
Lock(s) may refer to:
Common meanings
*Lock and key, a mechanical device used to secure items of importance
*Lock (water navigation), a device for boats to transit between different levels of water, as in a canal
Arts and entertainment
* ''Lock ...
acquired. Records removed this way cannot be restored in a rollback operation. Two notable exceptions to this rule are the implementations found in PostgreSQL and
Microsoft SQL Server
Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ...
, both of which allow TRUNCATE TABLE statements to be committed or rolled back transactionally.
* It is not possible to specify a WHERE clause in a TRUNCATE TABLE statement.
* TRUNCATE TABLE cannot be used when a foreign key references the table to be truncated, since TRUNCATE TABLE statements do not fire triggers. This could result in inconsistent data because ON DELETE/ON UPDATE triggers would not fire.
* In some computer systems, TRUNCATE TABLE resets the count of an Identity column back to the identity's ''seed''.
* In
Microsoft SQL Server
Microsoft SQL Server is a relational database management system developed by Microsoft. As a database server, it is a software product with the primary function of storing and retrieving data as requested by other software applications—which ...
2000 and beyond in full recovery mode, every change to the database is logged, so TRUNCATE TABLE statements can be used for tables involved in
log shipping Log shipping is the process of automating the backup of transaction log files on a primary (production) database server, and then restoring them onto a standby server. This technique is supported by Microsoft SQL Server,SQL keywords
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