Quick deletion of data from all tables in a database
Select ' TRUNCATE TABLE ' + name + '; ' from sysobjects where xtype= ' U ' ORDER by Name ASC;
After the execution of this statement, all the tables in the database are queried, and the TRUNCATE statement is executed after copying it.
sysobjects
Each object created within the database (constraints, default values, logs, rules, stored procedures, and so on) occupies a single row in the table. Only within tempdb , each temporary object occupies one row in the table.
Column Name |
Data Type |
Description |
Name |
sysname |
The name of the object. |
Id |
Int |
The object identification number. |
Xtype |
CHAR (2) |
The object type. Can be one of the following object types: C = CHECK Constraint D = defaults or DEFAULT constraints F = FOREIGN KEY constraint L = Log FN = Scalar function IF = Inline Table function P = Stored Procedure PK = PRIMARY KEY constraint (type is K) RF = copy Filter stored procedure S = System table TF = Table function TR = Trigger U = User Table UQ = UNIQUE constraint (type is K) V = view X = Extended Stored Procedure |
Uid |
smallint |
The user ID of the owner object. |
Info |
smallint |
Keep. Internal use only. |
Status |
Int |
Keep. Internal use only. |
Base_schema_ Ver |
Int |
Keep. Internal use only. |
Replinfo |
Int |
Keep. For replication use. |
Parent_obj |
Int |
The object identification number of the parent object (for example, for a trigger or constraint, which is the table ID). |
Crdate |
Datetime |
The date the object was created. |
Ftcatid |
smallint |
Full-text catalog identifier for all user tables registered for full-text indexing, or 0 for all user tables that are not registered. |
Schema_ver |
Int |
The version number, which is incremented each time the schema of the table changes. |
Stats_schema_ Ver |
Int |
Keep. Internal use only. |
Type |
CHAR (2) |
The object type. Can be one of the following values: C = CHECK Constraint D = defaults or DEFAULT constraints F = FOREIGN KEY constraint FN = Scalar function IF = Inline Table function K = PRIMARY KEY or UNIQUE constraint L = Log P = Stored Procedure R = Rule RF = copy Filter stored procedure S = System table TF = Table function TR = Trigger U = User Table V = view X = Extended Stored Procedure |
Userstat |
smallint |
Keep. |
Sysstat |
smallint |
Internal state information. |
Indexdel |
smallint |
Keep. |
Refdate |
Datetime |
reserved for later use. |
Version |
Int |
reserved for later use. |
Deltrig |
Int |
Keep. |
Instrig |
Int |
Keep. |
Updtrig |
Int |
Keep. |
Seltrig |
Int |
Keep. |
Category |
Int |
Used for publishing, constraints, and identification. |
Cache |
smallint |
Keep. |
Truncate and delete without a WHERE clause, and drop deletes the data in the table
Different points:
1. Truncate and delete only delete data without deleting the structure of the table (definition)
The drop statement will delete the structure of the table that is dependent on the constraint (constrain), trigger (trigger), index (indexed); Stored procedures/functions that depend on the table are preserved, but become invalid states.
The 2.delete statement is DML, which is placed in the rollback segement, which takes effect after the transaction is committed, and is triggered when the corresponding trigger is executed.
Truncate,drop is DDL, the operation takes effect immediately, the original data is not placed in the rollback segment and cannot be rolled back. Operation does not trigger trigger.
The 3.delete statement does not affect the extent occupied by the table, and the high waterline (watermark) remains in its original position.
Apparently the drop statement frees all the space occupied by the table.
Truncate statement by default see space released to minextents extent unless reuse storage is used; Truncate will reset the high watermark (back to the beginning).
4. Speed, in general: drop>; Truncate >; Delete
5. Security: Use Drop and truncate carefully, especially when there is no backup. Otherwise, it's too late to cry.
For use, to delete some data rows with delete, note the WHERE clause. The rollback segment should be large enough.
Want to delete the table, of course with drop
You want to keep the table and delete all the data. If it is unrelated to the transaction, use truncate. If it is related to a transaction, or if you want to trigger trigger, use Delete.
If you are defragmenting the inside of the table, you can use truncate to keep up with reuse stroage and re-import/Insert Data
Quickly delete data from all tables in a database