Mysql database: the difference between drop, truncate and delete

1、 Delete speed ：drop>truncate>delete;

2、 Delete by ：

• （1） perform delete In operation , Delete one row at a time from the table , At the same time, the deletion of this line is recorded in the log file .delete According to the where Conditions delete the specified in the table data , If you don't specify where Clause , Then follow truncate equally , You can delete all records in the table .
• （2）truncate Delete data by freeing the pages used to store table data , Delete all records in the table at once , The deleted data will not be recorded in the log file , Only the release of pages is recorded in the log file , Less system and transaction log resources used , So the execution speed is faster than delete fast . For tables referenced by foreign key constraints , Out of commission truncate table, Instead, it should be used without where Clause delete sentence .
• （3）drop Delete the structure and data of the entire table , But the constraints that are relied upon 、 trigger 、 Indexes 、 Stored procedures that depend on the table 、 The function will be reserved , But its state will change to invalid

3、 After deleting , Table and index space ：

• （1）delete The operation does not reduce the space occupied by the table or index ;
• （2） When the watch is truncate after , The space occupied by this table and index will be restored to the original size , But the structure of the table and its columns 、 constraint 、 The definition of the index remains unchanged .
• （3）drop Statement to free up all the space occupied by the table .

4、 submission ：delete yes DML, Manual submission is required to take effect , You can roll back , Triggers can be triggered ;truncate and drop yes DDL, Will implicitly submit , Cannot be rolled back , It doesn't trigger .

5、 Use scenarios ：

• （1） If you want to delete a table , Of course with drop;
• （2） If you want to keep the table and delete all the data , And it has nothing to do with transactions , use truncate that will do ;
• （3） If it's about business , Or want to trigger trigger, Or use it delete;

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