Curriculum
In this tutorial, you will learn how to use the SQL TRUNCATE TABLE statement to remove all data in a table efficiently and fast.
To delete all data from a table, you use the DELETE
 statement without a WHERE
 clause. For a big table that has few million rows, the DELETE
 statement is slow and not efficient.
To delete all rows from a big table fast, you use the following TRUNCATE TABLE
 statement:
TRUNCATE TABLE table_name;
In this syntax, you specify the table_name
 that you want to delete data after the TRUNCATE TABLE
 clause.
Some database systems such as MySQL and  PostgreSQL allow you to skip the TABLE
 keyword so the TRUNCATE TABLE
 statement is as simple as follows:
TRUNCATE table_name;
When you issue the TRUNCATE TABLE
 statement, the database system deletes all rows from the table by deallocating the data pages allocated by the table. By doing this, the RDBMS can reduce the resources for logging and the number of locks that need to acquire.
To truncate multiple tables at a time, you can use a list of comma-separated table names after the TRUNCATE TABLE
 clause as follows:
TRUNCATE TABLE table_name1, table_name2, ...;
Not all database systems support this form of the TRUNCATE TABLE
 statement. If you are using the one that does not, you must issue multiple TRUNCATE TABLE
 statements to truncate multiple tables.
Logically the TRUNCATE TABLE
 statement and the DELETE
 statement without the WHERE
 clause gives the same effect that removes all data from a table. However, they do have some differences:
DELETE
 statement, the database system logs the operations. And with some efforts, you can roll back the data that was deleted. However, when you use the TRUNCATE TABLE
 statement, you have no chance to roll back except you use it in a transaction that has not been committed.TRUNCATE TABLE
 statement. In this case, you must use the DELETE
 statement instead.TRUNCATE TABLE
 statement does not fire the delete trigger if the table has the triggers associated with it.TRUNCATE TABLE
 statement. It is not the case for the DELETE
 statement.DELETE
 statement with a WHERE
 clause deletes partial data from a table while the TRUNCATE TABLE
 statement always removes all data from the table.Let’s take a look at an example of truncating a table.
First, create a new table named big_table
 as follows:
CREATE TABLE big_table ( id INT AUTO_INCREMENT PRIMARY KEY, val INT );
Second, execute the following statement as many times as you want to insert sample data into the big_table
 table:
INSERT INTO big_table (val) VALUES (RAND(100000));
Note that if you use a database system that supports stored procedure, you can put this statement inside a loop. For example, the following stored procedure in MySQL loads data into the big_table
 table with the number of rows specified by the num
 parameter.
DELIMITER $$ CREATE PROCEDURE load_big_table_data(IN num int) BEGIN DECLARE counter int default 0; WHILE counter < num DO INSERT INTO big_table(val) VALUES(RAND(1000000)); END WHILE; END$$
The following statement calls the load_big_table_data
 stored procedure to insert 10,000 rows into the big_table
 table.
CALL load_big_table_data(10000);
Third, to remove all data from the big_table
, you use the following statement:
TRUNCATE TABLE big_table;
As you can see, how fast the TRUNCATE TABLE
 statement is.