The difference between TRUNCATE, DELETE and DROP is one of the most common interview questions that focus on SQL. The truncate statement is a data definition language or DDL command that is used to remove entire data from the table without deleting the structure of the table. There are many ways to delete data in SQL, including the DELETE, TRUNCATE TABLE, and DROP TABLE commands. In PostgreSQL, you need the TRUNC privilege; in SQL Server, the minimum permission is ALTER table; in MySQL, you need the DROP privilege.
The main distinction between them is that the delete statement erases data without restoring the identity of a table, while the truncate command restores the identity of a particular table. TRUNCATE TABLE locks the entire table to remove data from a table; thus, this command also uses less transaction space than DELETE. Note that we can't use the truncate statement when a foreign key references a table or participates in an indexed view. This tutorial will show you the difference between delete, truncate and drop statements in SQL Server.
TRUNCATE transactions can be undone in database engines such as SQL Server and PostgreSQL, but not in MySQL and Oracle. The truncate command unmaps pages instead of rows and creates an entry for deallocation pages instead of rows in transaction logs. When it comes to deleting data from a database table, there are three main commands: DELETE, TRUNCATE and DROP. Each of these commands has its own purpose and should be used accordingly.
The DELETE command is used to delete specific rows from a table, while TRUNCATE is used to delete all rows from a table. The DROP command is used to delete an entire table from a database. The DELETE command is slower than TRUNCATE as it deletes rows one by one and records an entry for each deleted row in the transaction log. On the other hand, TRUNCATE deletes all rows at once and only records one entry in the transaction log.
This makes it faster than DELETE as it requires less I/O operations. However, it should be noted that TRUNCATE cannot be used when there are foreign keys referencing the table or when it participates in an indexed view. It removes both the data and structure of the table from the database permanently and cannot be undone. Therefore, it should be used with caution as it cannot be reversed once executed.
In conclusion, each of these commands has its own purpose and should be used accordingly. The DROP command is used to delete an entire table from a database.