The primary difference between DELETE and TRUNCATE lies in how they remove data from tables within a database. DELETE is a SQL command that removes specific rows from a table based on a condition specified in a WHERE clause, allowing for selective deletions. For example, running a command like DELETE FROM employees WHERE employee_id = 10; will only remove the employee with the ID of 10. This command can be rolled back if it's executed within a transaction, provided it hasn't been committed yet, which adds a layer of safety.
On the other hand, TRUNCATE is a more aggressive command used to remove all rows from a table without the option to specify conditions. It effectively resets the table to its empty state and does so without logging individual row deletions, which can result in better performance when dealing with large datasets. For instance, executing TRUNCATE TABLE employees; will remove all entries in the employees table in one operation, which is faster than a DELETE operation that processes each row individually. However, it is important to note that TRUNCATE cannot be rolled back if it is executed outside of a transaction.
Another important distinction is that TRUNCATE resets any auto-increment counters associated with the table, meaning if you have an ID column that auto-increments, the next insert will start from the initial value again. In contrast, the DELETE command does not affect these counters, and subsequent inserts will continue from where they left off. Therefore, while both commands serve the purpose of data removal, they are suited to different use cases and have different implications for performance, transaction safety, and table structure.