(SQL Tutorials for Citizen Data Scientist)
SQL TRUNCATE TABLE Statement
In this tutorial you will learn how to quickly delete all rows from a table using SQL.
Removing Table Data
The TRUNCATE TABLE
statement removes all the rows from a table more quickly than a DELETE
. Logically, TRUNCATE TABLE
is similar to the DELETE
statement with no WHERE
clause.
The TRUNCATE TABLE
statement removes all the rows from a table, but the table structure and its columns, constraints, indexes, and so on remain intact. To remove the table definition in addition to its data, you can use the DROP TABLE
statement.
Syntax
The basic syntax of TRUNCATE TABLE
can be given with:
table_name
;Let’s perform the truncate operation on a database table.
Consider we’ve an employees table in our database with the following records:
+--------+--------------+------------+--------+---------+ | emp_id | emp_name | hire_date | salary | dept_id | +--------+--------------+------------+--------+---------+ | 1 | Ethan Hunt | 2001-05-01 | 5000 | 4 | | 2 | Tony Montana | 2002-07-15 | 6500 | 1 | | 3 | Sarah Connor | 2005-10-18 | 8000 | 5 | | 4 | Rick Deckard | 2007-01-03 | 7200 | 3 | | 5 | Martin Blank | 2008-06-24 | 5600 | NULL | +--------+--------------+------------+--------+---------+
The following command removes all the rows from the employees table:
Example
TRUNCATE TABLE employees;
Now, after executing the above SQL statement, if you try to select the records from the employees table, you will get an empty result set.
TRUNCATE TABLE vs DELETE
Although DELETE
and TRUNCATE TABLE
seem to have the same effect, but they do work differently. Here are some major differences between these two statements:
TRUNCATE TABLE
statement drop and re-create the table in such a way that any
auto-increment value is reset to its start value which is generally 1.DELETE
lets you filter which rows to be deleted based upon an optionalWHERE
clause, whereasTRUNCATE TABLE
doesn’t supportWHERE
clause it just removes all the rows.TRUNCATE TABLE
is faster and uses fewer system resources thanDELETE
, becauseDELETE
scans the table to generate a count of rows that were affected then delete the rows one by one and records an entry in the database log for each deleted row, whileTRUNCATE TABLE
just delete all the rows without providing any additional information.
Beginners Guide to SQL – SQL TRUNCATE TABLE Statement
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