Detailed explanation of how to delete table data in Oracle database

Oracle database is a very powerful management database software. It can store massive amounts of data, manage multiple users, and provide high availability and reliability of data. In the daily work of database administrators, deleting table data is a very common operation. Today let us learn how to delete table data in Oracle database.

1. Confirm the deleted table data

Before deleting the table data, you must first confirm which table data needs to be deleted. You can use the SELECT statement to query the table data that needs to be deleted. For example, if we need to delete all employee records with a salary greater than 5,000 in the table named "employees", we can use the following SQL statement:

SELECT * FROM employees WHERE salary > 5000;

This SQL statement will display all employee records with a salary greater than 5,000.

2. Delete table data

There are many ways to delete table data in Oracle database. In this article, we'll cover two of the common methods.

(1) Use the DELETE statement to delete table data

You can use the DELETE statement to delete table data. The WHERE clause in the DELETE statement specifies the table data that needs to be deleted.

For example, we can use the following SQL statement to delete all employee records with a salary greater than 5,000 in the table named "employees":

DELETE FROM employees WHERE salary > 5000;

This SQL statement will delete all employees with a salary greater than 5,000 Record.

(2) Use the TRUNCATE TABLE statement to delete table data

The TRUNCATE TABLE statement can quickly delete all data in the table. The TRUNCATE TABLE statement does not delete data from the table row by row (slower than the DELETE statement), but deletes the entire table at once.

For example, we can use the following SQL statement to delete all data in the table named "employees":

TRUNCATE TABLE employees;

This SQL statement will immediately delete all data in the table named "employees" .

3. Confirm the deleted table data

Before executing the DELETE or TRUNCATE TABLE statement, you need to confirm the table data to be deleted again. This is very important because once data is deleted, they cannot be recovered.

You can use the SELECT statement to reconfirm the table data that needs to be deleted. For example, if we need to reconfirm the deletion of all employee records with a salary greater than 5,000 in the table named "employees", we can use the following SQL statement:

SELECT * FROM employees WHERE salary > 5000;

This SQL statement will display all employee records with a salary greater than 5,000 . If you confirm that you need to delete these employee records, you can execute the DELETE or TRUNCATE TABLE statement to delete these records.

4. Back up data

Before deleting table data, you should back up the data that needs to be deleted. Data backup is very important because once data is deleted, they cannot be restored. The easiest way to back up your data is to export the table data to a file, which can be done using Oracle's data export tool (such as expdp).

5. Conclusion

In Oracle database, deleting table data is a very common operation. Before deleting table data, you need to confirm which table data needs to be deleted, and then execute the DELETE or TRUNCATE TABLE statement to delete the data after confirmation. Before deleting data, be sure to back it up so that you can restore it if needed.

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