How to perform table deletion and recovery operations in Oracle database

Oracle database is a relational database management system that can easily store and manage large amounts of data. When using Oracle database, we may often need to delete tables, but sometimes we delete a table by mistake, or find that it needs to be restored after deleting a table. What should we do in this case? This article will introduce how to perform table deletion and recovery operations in Oracle database.

1. Use the FLASHBACK TABLE command to restore

FLASHBACK TABLE is a method provided by Oracle database to restore deleted tables. Use the FLASHBACK TABLE command to restore a deleted table to a specified point in time without any backup operations. The following are the specific steps:

1. First, you need to confirm whether the current Flashback function is turned on. You can confirm with the following command:

SQL> show parameter flashback;

If flashback_on is displayed as TRUE, the function has been turned on, otherwise you need to use the following command to turn it on:

SQL> alter database flashback on;

2. Use the FLASHBACK TABLE command to restore the table. As shown below:

SQL> FLASHBACK TABLE table_name TO TIMESTAMP TO_TIMESTAMP('2022-03-01 14:00:00', 'YYYY-MM-DD HH24:MI:SS');

Among them, table_name represents the name of the table that needs to be restored, and the TO_TIMESTAMP() function is used to specify the time point that needs to be restored.

2. Use Recycle Bin for recovery

Recycle Bin is a mechanism provided by Oracle database to recover deleted tables. Through this mechanism, Oracle will store the deleted tables in the Recycle Bin, and we can find and restore the deleted tables in the Recycle Bin. The specific steps are as follows:

1. Check which deleted tables exist in the Recycle Bin. As shown below:

SQL> show recyclebin;

2. Restore the specified table. As shown below:

SQL> flashback table "BIN$table_name" to before drop;

where table_name represents the name of the table that needs to be restored.

It should be noted that if we use the PURGE command to delete the table from the Recycle Bin before deleting the table, the table will not be restored through the Recycle Bin, and we need to use other recovery methods. .

3. Use Undo table space for recovery

If we do not enable the Flashback function and do not use Recycle Bin for backup, then we can also use the Undo table space to restore the table. Undo tablespace is a tablespace used by Oracle database to manage data modification history. When deleting data, Oracle will save the data modification history to the Undo tablespace. We can restore deleted data through the data in the Undo tablespace. table. The specific steps are as follows:

1. Query the SCN number of the deleted table. As shown below:

SQL> select max(SCN) from table_name;

where table_name represents the name of the table that needs to be restored.

2. Restore the table by specifying the SCN number. As shown below:

SQL> flashback table table_name to SCN 1234567;

Among them, table_name represents the table name that needs to be restored, and SCN represents the SCN number that needs to be restored.

Summary

In the Oracle database, we can use a variety of methods to perform table deletion and recovery operations, such as using the FLASHBACK TABLE command, Recycle Bin and Undo table space. When deleting a table, you need to pay attention to the backup operation in case of emergency. In the actual production environment, we should operate with caution to ensure that no unnecessary deletion operations are performed accidentally or unintentionally, so as to ensure the integrity and reliability of the data.

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