What s the difference between TRUNCATE and DELETE in SQL

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What s the difference between TRUNCATE and DELETE in SQL   If your answer is platform specific  please indicate that

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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   The Syntax of a SQL DELETE statement is   DELETE FROM table name  WHERE condition    TRUNCATE statement  This command is used to delete all the rows from the table and free the space containing the table

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Yes  DELETE is slower  TRUNCATE is faster  Why    DELETE must read the records  check constraints  update the block  update indexes  and generate redo undo  All of that takes time   TRUNCATE simply adjusts a pointer in the database for the table  the High Water Mark  and poof  the data is gone    This is Oracle specific  AFAIK

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Truncate doesn t log anything  is correct   I d go further   Truncate is not executed in the context of a transaction     The speed advantage of truncate over delete should be obvious   That advantage ranges from trivial to enormous  depending on your situation   However  I ve seen truncate unintentionally break referential integrity   and violate other constraints   The power that you gain by modifying data outside a transaction has to be balanced against the responsibility that you inherit when you walk the tightrope without a net

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One further difference of the two operations is that if the table contains an identity column  the counter for that column is reset 1  or to the seed value defined for the column  under TRUNCATE  DELETE does not have this affect

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DELETE The DELETE command is used to remove rows from a table  A WHERE clause can be used to only remove some rows  If no WHERE condition is specified  all rows will be removed  After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it  Note that this operation will cause all DELETE triggers on the table to fire  TRUNCATE TRUNCATE removes all rows from a table  The operation cannot be rolled back and no triggers will be fired  As such  TRUCATE is faster and doesn t use as much undo space as a DELETE  DROP The DROP command removes a table from the database  All the tables  rows  indexes and privileges will also be removed  No DML triggers will be fired  The operation cannot be rolled back   DROP and TRUNCATE are DDL commands  whereas DELETE is a DML command  Therefore DELETE operations can be rolled back  undone   while DROP and TRUNCATE operations cannot be rolled back   From  http   www orafaq com faq difference between truncate delete and drop commands

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A small correction to the original answer - delete also generates significant amounts of redo  as undo is itself protected by redo    This can be seen from autotrace output   SQL gt  delete from t1   10918 rows deleted   Elapsed  00 00 00 58  Execution Plan ----------------------------------------------------------    0      DELETE STATEMENT Optimizer FIRST ROWS  Cost 43 Card 1     1    0   DELETE OF  T1     2    1     TABLE ACCESS  FULL  OF  T1   TABLE   Cost 43 Card 1      Statistics ----------------------------------------------------------          30  recursive calls       12118  db block gets         213  consistent gets         142  physical reads     3975328  redo size         441  bytes sent via SQL Net to client         537  bytes received via SQL Net from client           4  SQL Net roundtrips to from client           2  sorts  memory            0  sorts  disk        10918  rows processed

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Here s a list of differences  I ve highlighted Oracle-specific features  and hopefully the community can add in other vendors  specific difference also  Differences that are common to most vendors can go directly below the headings  with differences highlighted below     General Overview  If you want to quickly delete all of the rows from a table  and you re really sure that you want to do it  and you do not have foreign keys against the tables  then a TRUNCATE is probably going to be faster than a DELETE   Various system-specific issues have to be considered  as detailed below     Statement type  Delete is DML  Truncate is DDL  What is DDL and DML      Commit and Rollback  Variable by vendor  SQL Server  Truncate can be rolled back   PostgreSQL  Truncate can be rolled back   Oracle  Because a TRUNCATE is DDL it involves two commits  one before and one after the statement execution  Truncate can therefore not be rolled back  and a failure in the truncate process will have issued a commit anyway   However  see Flashback below     Space reclamation  Delete does not recover space  Truncate recovers space  Oracle  If you use the REUSE STORAGE clause then the data segments are not de-allocated  which can be marginally more efficient if the table is to be reloaded with data  The high water mark is reset     Row scope  Delete can be used to remove all rows or only a subset of rows  Truncate removes all rows   Oracle  When a table is partitioned  the individual partitions can be truncated in isolation  thus a partial removal of all the table s data is possible     Object types  Delete can be applied to tables and tables inside a cluster  Truncate applies only to tables or the entire cluster   May be Oracle specific     Data Object Identity  Oracle  Delete does not affect the data object id  but truncate assigns a new data object id unless there has never been an insert against the table since its creation Even a single insert that is rolled back will cause a new data object id to be assigned upon truncation     Flashback  Oracle   Flashback works across deletes  but a truncate prevents flashback to states prior to the operation   However  from 11gR2 the FLASHBACK ARCHIVE feature allows this  except in Express Edition  Use of FLASHBACK in Oracle http   docs oracle com cd E11882 01 appdev 112 e41502 adfns flashback htm ADFNS638    Privileges  Variable  Oracle  Delete can be granted on a table to another user or role  but truncate cannot be without using a DROP ANY TABLE grant     Redo Undo  Delete generates a small amount of redo and a large amount of undo  Truncate generates a negligible amount of each     Indexes  Oracle  A truncate operation renders unusable indexes usable again  Delete does not     Foreign Keys  A truncate cannot be applied when an enabled foreign key references the table  Treatment with delete depends on the configuration of the foreign keys     Table Locking  Oracle  Truncate requires an exclusive table lock  delete requires a shared table lock  Hence disabling table locks is a way of preventing truncate operations on a table     Triggers  DML triggers do not fire on a truncate   Oracle  DDL triggers are available     Remote Execution  Oracle  Truncate cannot be issued over a database link     Identity Columns  SQL Server  Truncate resets the sequence for IDENTITY column types  delete does not     Result set  In most implementations  a DELETE statement can return to the client the rows that were deleted   e g  in an Oracle PL SQL subprogram you could   DELETE FROM employees temp WHERE       employee id   299  RETURNING   first name              last name INTO        emp first name              emp last name

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In SQL Server 2005 I believe that you can rollback a truncate

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Truncate command is used to re-initialize the table  it is a DDL command which delete all the rows of table Whereas DELETE is a DML command which is used to delete row or set of rows according to some condition  if condition is not specified then this command will delete all the rows from the table

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DELETE statement can have a WHERE clause to delete specific records whereas TRUNCATE statement does not require any and wipes the entire table  Importantly  the DELETE statement logs the deleted date whereas the TRUNCATE statement does not

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TRUNCATE is fast  DELETE is slow   Although  TRUNCATE has no accountability

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The difference between truncate and delete is listed below    ---------------------------------------- ----------------------------------------------                   Truncate                                     Delete                       ---------------------------------------- ----------------------------------------------    We can t Rollback after performing       We can Rollback after delete                     Truncate                                                                                                                                                                            Example                                  Example                                          BEGIN TRAN                               BEGIN TRAN                                       TRUNCATE TABLE tranTest                  DELETE FROM tranTest                             SELECT   FROM tranTest                   SELECT   FROM tranTest                           ROLLBACK                                 ROLLBACK                                         SELECT   FROM tranTest                   SELECT   FROM tranTest                          ---------------------------------------- ----------------------------------------------    Truncate reset identity of table         Delete does not reset identity of table         ---------------------------------------- ----------------------------------------------    It locks the entire table                It locks the table row                          ---------------------------------------- ----------------------------------------------    Its DDL Data Definition Language         Its DML Data Manipulation Language               command                                  command                                         ---------------------------------------- ----------------------------------------------    We can t use WHERE clause with it        We can use WHERE to filter data to delete       ---------------------------------------- ----------------------------------------------    Trigger is not fired while truncate      Trigger is fired                                ---------------------------------------- ----------------------------------------------    Syntax                                   Syntax                                           1  TRUNCATE TABLE table name             1  DELETE FROM table name                                                                 2  DELETE FROM table name WHERE                                                              example column id IN  1 2 3                  ---------------------------------------- ----------------------------------------------

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It is not that truncate does not log anything in SQL Server  truncate does not log any information but it log the deallocation of data page for the table on which you fired TRUNCATE   and truncated record can be rollback if we define transaction at beginning and we can recover the truncated record after rollback it  But can not recover truncated records from the transaction log backup after committed truncated transaction

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By issuing a TRUNCATE TABLE statement  you are instructing SQL Server to delete every record within a table  without any logging or transaction processing taking place

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TRUNCATE is the DDL statement whereas DELETE is a DML statement  Below are the differences between the two      As TRUNCATE is a DDL  Data definition language  statement it does not require a commit to make the changes permanent  And this is the reason why rows deleted by truncate could not be rollbacked  On the other hand DELETE is a DML  Data manipulation language  statement hence requires explicit commit to make its effect permanent  TRUNCATE always removes all the rows from a table  leaving the table empty and the table structure intact whereas DELETE may remove conditionally if the where clause is used  The rows deleted by TRUNCATE TABLE statement cannot be restored and you can not specify the where clause in the TRUNCATE statement  TRUNCATE statements does not fire triggers as opposed of on delete trigger on DELETE statement   Here is the very good link relevant to the topic

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In short  truncate doesn t log anything  so is much faster but can t be undone  whereas delete is logged  and can be part of a larger transaction  will rollback etc   If you have data that you don t want in a table in dev it is normally better to truncate as you don t run the risk of filling up the transaction log

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DROP The DROP command removes a table from the database  All the tables  rows  indexes and privileges will also be removed  No DML triggers will be fired  The operation cannot be rolled back  TRUNCATE TRUNCATE removes all rows from a table  The operation cannot be rolled back and no triggers will be fired  As such  TRUNCATE is faster and doesn t use as much undo space as a DELETE  Table level lock will be added when Truncating  DELETE The DELETE command is used to remove rows from a table  A WHERE clause can be used to only remove some rows  If no WHERE condition is specified  all rows will be removed  After performing a DELETE operation you need to COMMIT or ROLLBACK the transaction to make the change permanent or to undo it  Note that this operation will cause all DELETE triggers on the table to fire  Row level lock will be added when deleting   From  http   www orafaq com faq difference between truncate delete and drop commands

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The biggest difference is that truncate is non logged operation while delete is   Simply it means that in case of a database crash   you cannot recover the data operated upon by truncate but with delete you can    More details here

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DELETE   DELETE is a DML command DELETE you can rollback Delete   Only Delete- so it can be rolled back In DELETE you can write conditions using WHERE clause Syntax     Delete from  Table  where  Condition     TRUNCATE   TRUNCATE is a DDL command You can t rollback in TRUNCATE  TRUNCATE removes the record permanently Truncate   Delete Commit -so we can t roll back You can t use conditions WHERE clause  in TRUNCATE Syntax     Truncate table  Table     For more details visit  http   www zilckh com what-is-the-difference-between-truncate-and-delete

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All good answers  to which I must add   Since TRUNCATE TABLE is a DDL  Data Defination Language   not a DML  Data Manipulation Langauge  command  the Delete Triggers do not run

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Truncate  can also be Rollbacked  here  the  exapmle  begin Tran delete from  Employee  select   from Employee Rollback select   from Employee

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I d comment on matthieu s post  but I don t have the rep yet     In MySQL  the auto increment counter gets reset with truncate  but not with delete

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A big reason it is handy  is when you need to refresh the data in a multi-million row table  but don t want to rebuild it    Delete    would take forever  whereas the perfomance impact of Truncate would be negligible

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Truncate and Delete in SQL are two commands which is used to remove or delete data from table  Though quite basic in nature both Sql commands can create lot of trouble until you are familiar with details before using it  An Incorrect choice of command can result is either very slow process or can even blew up log segment  if too much data needs to be removed and log segment is not enough  That s why it s critical to know when to use truncate and delete command in SQL but before using these you should be aware of the Differences between Truncate and Delete  and based upon them  we should be able to find out when DELETE is better option for removing data or TRUNCATE should be used to purge tables   Refer check click here

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TRUNCATE can be rolled back if wrapped in a transaction    Please see the two references below and test yourself -  http   blog sqlauthority com 2007 12 26 sql-server-truncate-cant-be-rolled-back-using-log-files-after-transaction-session-is-closed    http   sqlblog com blogs kalen delaney archive 2010 10 12 tsql-tuesday-11-rolling-back-truncate-table aspx  The TRUNCATE vs  DELETE is one of the infamous questions during SQL interviews  Just make sure you explain it properly to the Interviewer or it might cost you the job  The problem is that not many are aware so most likely they will consider the answer as wrong if you tell them that YES Truncate can be rolled back

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One more difference specific to microsoft sql server is with delete you can use output statement to track what records have been deleted  e g    delete from  SomeTable  output deleted Id  deleted Name   You cannot do this with truncate

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If accidentally you removed all the data from table using Delete Truncate  You can rollback committed transaction  Restore the last backup and run transaction log till the time when Delete Truncate is about to happen   The related information below is from a blog post      While working on database  we are using Delete and Truncate without   knowing the differences between them  In this article we will discuss   the difference between Delete and Truncate in Sql       Delete          Delete is a DML command    Delete statement is executed using a row lock each row in the table is locked for deletion    We can specify filters in where clause    It deletes specified data if where condition exists    Delete activities a trigger because the operation are logged individually    Slower than Truncate because it Keeps logs         Truncate         Truncate is a DDL command    Truncate table always lock the table and page but not each row As it removes all the data    Cannot use Where condition     It Removes all the data    Truncate table cannot activate a trigger because the operation does not log individual row deletions    Faster in performance wise  because it doesn t keep any logs          Note  Delete and Truncate both can be rolled back when used with   Transaction  If Transaction is done  means committed then we can not   rollback Truncate command  but we can still rollback Delete command   from Log files  as delete write records them in Log file in case it is   needed to rollback in future from log files       If you have a Foreign key constraint referring to the table you are   trying to truncate  this won t work even if the referring table has no   data in it  This is because the foreign key checking is done with DDL   rather than DML  This can be got around by temporarily disabling the   foreign key constraint s  to the table       Delete table is a logged operation  So the deletion of each row gets   logged in the transaction log  which makes it slow  Truncate table   also deletes all the rows in a table  but it won t log the deletion of   each row instead it logs the deallocation of the data pages of the   table  which makes it faster         If accidentally you removed all the data from table using   Delete Truncate  You can rollback committed transaction  Restore the   last backup and run transaction log till the time when Delete Truncate   is about to happen

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Here is my detailed answer on the difference between DELETE and TRUNCATE in SQL Server        Remove Data    First thing first  both can be used to remove the rows from table  But a DELETE can be used to remove the rows not only from a Table but also from a VIEW or the result of an OPENROWSET or OPENQUERY subject to provider capabilities          FROM Clause   With DELETE you can also delete rows from one table view rowset function limited based on rows from another table by using another FROM clause   In that FROM clause you can also write normal JOIN conditions   Actually you can create a DELETE statement from a SELECT statement that doesn   t contain any aggregate functions by replacing SELECT with DELETE and removing column names  With TRUNCATE you can   t do that          WHERE   A TRUNCATE cannot have WHERE Conditions  but a DELETE can   That means with TRUNCATE you can   t delete a specific row or specific group of rows   TRUNCATE TABLE is similar to the DELETE statement with no WHERE clause         Performance   TRUNCATE TABLE is faster and uses fewer system and transaction log resources   And one of the reason is locks used by either statements  The DELETE statement is executed using a row lock  each row in the table is locked for deletion  TRUNCATE TABLE always locks the table and page but not each row         Transaction log   DELETE statement removes rows one at a time and makes individual entries in the transaction log for each row  TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log         Pages   After a DELETE statement is executed  the table can still contain empty pages   TRUNCATE removes the data by deallocating the data pages used to store the table data         Trigger   TRUNCATE does not activate the delete triggers on the table   So you must be very careful while using TRUNCATE   One should never use a TRUNCATE if delete Trigger is defined on the table to do some automatic cleanup or logging action when rows are deleted         Identity Column   With TRUNCATE if the table contains an identity column  the counter for that column is reset to the seed value defined for the column   If no seed was defined  the default value 1 is used   DELETE doesn   t reset the identity counter   So if you want to retain the identity counter  use DELETE instead         Replication   DELETE can be used against table used in transactional replication or merge replication  While TRUNCATE cannot be used against the tables involved in transactional replication or merge replication          Rollback   DELETE statement can be rolled back  TRUNCATE can also be rolled back provided it is enclosed in a TRANSACTION block and session is not closed   Once session is closed you won t be able to Rollback TRUNCATE         Restrictions   The DELETE statement may fail if it violates a trigger or tries to remove a row referenced by data in another table with a FOREIGN KEY constraint  If the DELETE removes multiple rows  and any one of the removed rows violates a trigger or constraint  the statement is canceled  an error is returned  and no rows are removed  And if DELETE is used against View  that View must be an Updatable view   TRUNCATE cannot be used against the table used in Indexed view  TRUNCATE cannot be used against the table referenced by a FOREIGN KEY constraint  unless a table that has a foreign key that references itself

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Can t do DDL over a dblink

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Summary of Delete Vs Truncate in SQL server For Complete Article follow this link   http   codaffection com sql-server-article delete-vs-truncate-in-sql-server     Taken from dotnet mob article  Delete Vs Truncate in SQL Server

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With SQL Server or MySQL  if there is a PK with auto increment  truncate will reset the counter

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TRUNCATE  TRUNCATE SQL query removes all rows from a table  without logging the individual row deletions     TRUNCATE is a DDL command  TRUNCATE is executed using a table lock and whole table is locked for remove all records  We cannot use WHERE clause with TRUNCATE  TRUNCATE removes all rows from a table  Minimal logging in transaction log  so it is faster performance wise  TRUNCATE TABLE removes the data by deallocating the data pages used to store the table data and records only the page deallocations in the transaction log  To use Truncate on a table you need at least ALTER permission on the table  Truncate uses less transaction space than the Delete statement  Truncate cannot be used with indexed views  TRUNCATE is faster than DELETE    DELETE  To execute a DELETE queue  delete permissions are required on the target table  If you need to use a WHERE clause in a DELETE  select permissions are required as well    DELETE is a DML command  DELETE is executed using a row lock  each row in the table is locked for deletion  We can use where clause with DELETE to filter  amp  delete specific records  The DELETE command is used to remove rows from a table based on WHERE condition  It maintain the log  so it slower than TRUNCATE  The DELETE statement removes rows one at a time and records an entry in the transaction log for each deleted row  Identity of column keep DELETE retains the identity  To use Delete you need DELETE permission on the table  Delete uses the more transaction space than Truncate statement  Delete can be used with indexed views

[sql] What's the difference between TRUNCATE and DELETE in SQL

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