When working with databases, one of the most common tasks is to remove data from a table. This can be done through the use of two SQL commands: TRUNCATE and DELETE. While both of these commands achieve the same end result, there are some key differences between them that every database developer should understand.
TRUNCATE and DELETE are both known as Data Manipulation Language (DML) commands in SQL. DML commands are used to modify data within a database, as opposed to Data Definition Language (DDL) commands which are used to create, alter, and drop database objects such as tables and views. Now let's dive into the specifics of TRUNCATE and DELETE.
TRUNCATE is a command used to remove all rows from a table. This means that the table structure and columns remain intact, but all data is deleted. One of the main differences between TRUNCATE and DELETE is that TRUNCATE does not use a WHERE clause. This means that it cannot selectively delete specific rows from a table. Instead, it deletes all rows in one go, making it a much faster operation than DELETE.
On the other hand, the DELETE command is used to remove specific rows from a table based on a given condition. This condition is specified using the WHERE clause. This allows for more control over which rows are deleted from a table. However, this also means that DELETE is a slower operation compared to TRUNCATE, as it has to evaluate the WHERE clause for each row before deciding whether to delete it or not.
Another important difference between TRUNCATE and DELETE is that TRUNCATE resets the identity values of the table, whereas DELETE does not. Identity values are used to uniquely identify each row in a table, and when a row is deleted, its identity value remains unchanged. However, when a table is truncated, the identity values are reset to their initial seed value. This can be useful when working with auto-incrementing identity columns.
It's important to note that TRUNCATE cannot be used on tables that have foreign key constraints. Foreign key constraints are used to maintain referential integrity between tables. When a row is deleted from a table that has a foreign key constraint, the corresponding rows in other tables are also deleted. Since TRUNCATE deletes all rows in one go, it cannot be used on tables with foreign key constraints as it would also delete the related rows in other tables.
On the other hand, DELETE can be used on tables with foreign key constraints. However, it's important to be cautious when using DELETE on tables with foreign key constraints as it can lead to orphaned rows in related tables if not used carefully.
In summary, TRUNCATE and DELETE are two SQL commands used to remove data from tables. TRUNCATE is a faster operation as it deletes all rows in one go, but it cannot be used with tables that have foreign key constraints. DELETE, on the other hand, is a slower operation that can be used on tables with foreign key constraints, but it allows for more control over which rows are deleted. It's important for database developers to understand the differences between these two commands in order to use them effectively in their projects.
