What is the difference in Truncate and Delete in SQL?

Truncate is the DDL command in sql used to delete the entire table content ant not the table structure. Truncate command followed by commit command means as we fire truncate command it delete the content of table and free the memory space held by rows of that table and we can not roll back. Delete is the DML command in SQL used to delete the content of Table. as we fire the Delete command it will delete the content of table even we can specifie the condition to delete the rows (content) of table. We can rollback after firing Delete command as it is a DML command. read less

1>TRUNCATE is a DDL command whereas DELETE is a DML command. 2>TRUNCATE is much faster than DELETE. Reason:When you type DELETE.all the data get copied into the Rollback Tablespace first.then delete operation get performed.Thatswhy when you type ROLLBACK after deleting a table ,you can get back the data(The system get it for you from the Rollback Tablespace).All this process take time.But when you type TRUNCATE,it removes data directly without copying it into the Rollback Tablespace.Thatswhy TRUNCATE is faster.Once you Truncate you cann't get back the data. 3>You cann't rollback in TRUNCATE but in DELETE you can rollback.TRUNCATE removes the record permanently. 4>In case of TRUNCATE ,Trigger doesn't get fired.But in DML commands like DELETE .Trigger get fired. 5>You cann't use conditions(WHERE clause) in TRUNCATE.But in DELETE you can write conditions using WHERE clause read less

DELETE Statement is used to delete rows from a table. Syntax : DELETE FROM table_name [WHERE condition]; table_name -- the table name which has to be updated. TRUNCATE command is used to delete all the rows from the table and free the space containing the table. Syntax: TRUNCATE TABLE table_name; DELETE Statement: This command deletes only the rows from the table based on the condition given in the where clause or deletes all the rows from the table if no condition is specified. But it does not free the space containing the table. TRUNCATE statement: This command is used to delete all the rows from the table and free the space containing the table. read less

Objective of using Truncate command is to remove the entity set from the database and freeing the corresponding memory space. It can't be rolled back. Its a data definition command. delete command deletes records from an entity set. it may delete all the records , still the table would exist.Its a data manipulation command as it cannot make any change in the structure of the table. read less

In SQL Server there are a couple a ways you can delete rows from a table. You can use the TRUNCATE and DELETE command. Though the end result of both commands is the same, there are very important differences you should know about. The TRUNCATE command is like a DELETE command without the WHERE clause with much less of a safety net. When to use TRUNCATE When you TRUNCATE a table less information is logged. This means the TRUNCATE statement executes very fast; however, it does so at the expense of not logging each row deleted. This means, that you need to be very careful when using the command (actually be careful with DELETE as well!). Though you are able to rollback a TRUNCATE command in SQL Server, you can not do the same in Oracle. The TRUNCATE command is simple yet extremely dangerous. Here is an example to remove all rows from the employee table: TRUNCATE TABLE employee If you mistakenly execute a TRUNCATE statement, it is much more difficult to recover, and you may loose data in the process. The TRUNCATE command does log the pages it removes, so it is possible to recover the pages using some advanced code. Here are some reasons to use TRUNCATE: You want to “reset” a table to its empty state. All rows are removed, and identity key values reset to the initial defined values. You need to have a super quick way of clearing out table data. I can see this occurring when you need to repeatedly import test data or you have routines that use work tables or scratch tables to store information. You want to remove rows from a table without activating the table’s after delete trigger. Keep in mind that TRUNCATE will lock the table, so obviously don’t use this command on a table being shared by many concurrent users. When to use the DELETE command The DELETE command is used to remove records from a database. It is the most common way to do so. In its simplest form you can remove all the rows from a database or you can add a WHERE clause to remove only those meeting the criteria. When execute the DELETE command,the DBMS logs all removed rows. This means it is easier to recover from a mistake, than it would a mistaken TRUNCATE. The command DELETE FROM employee Will remove all employees from the employee table; whereas, DELETE FROM employee WHERE firstName = ‘Kris’ deletes all employees whose first name is Kris. I would pretty much recommend using a DELETE statement in all cases, except for those special circumstances that merit a TRUNCATE. Here are some things that happen during a DELETE that don’t during the TRUNCATE: Any deletion triggers are executed on the affected table. You are allowed to DELETE records that have foreign key constraints defined. A TRUNCATE cannot be executed if these same constraints are in place. Record deletions don’t reset identity keys. This is important when you need to guarantee each row uses a key that has never been used before. Perhaps, this need to happen for audit reasons. Depending on the locking you are using, row locks are placed on deleteddeleted rows. Unaffected rows remain unlocked. Conclusion I should point out that TURNCATE is considered a DDL command; whereas, DELETE is DML. I think this distinction should help you further understand when to use either command and the implications for doing so. In a nutshell use DELETE to remove one or more rows from a table. Only in special situation, such as when you need to reset a table to its initial state should you consider TRUNCATE. read less

DELETE: This command is used to delete rows from a table. a) Where Clause: If you give where Clause rows depending on that where clause would get deleted. b) Without Where Clause: If you do not give where clause all the rows would get deleted from a table. DELETE is a DML command, hence it can be rollback. DELETE does not frees the space from a table. TRUNCATE: This command is used to delete all records from a table. TRUNCATE is a DDL command, hence it can't be rollback. TRUNCATE command frees the space from a table. read less