In the SQL (Structured Query Language) command-line interface (CLI), deleting data from a database involves using the DELETE statement. This statement allows you to remove one or more rows from a table based on specified conditions.

Syntax

The basic syntax for the DELETE statement in SQL is as follows:

DELETE FROM table_name
WHERE condition;

Here, table_name is the name of the table from which you want to delete data. The WHERE clause is optional and is used to specify the conditions that must be met for the deletion to take place.

Deleting all rows in a table

If you want to delete all rows from a table, you can use the DELETE statement without the WHERE clause. Here’s an example:

DELETE FROM employees;

This will delete all rows from the employees table.

Deleting specific rows based on conditions

To delete specific rows based on conditions, you need to use the WHERE clause. For example, if you want to delete all employees whose salary is less than 50000, you can use the following query:

DELETE FROM employees
WHERE salary < 50000;

This will delete all rows from the employees table where the salary is less than 50000.

Deleting data in batches

In some cases, you may need to delete data in batches to avoid locking the table for an extended period. You can achieve this by using the LIMIT clause in combination with the DELETE statement. For example, to delete 100 rows at a time from the employees table, you can use the following query:

DELETE FROM employees
WHERE some_condition
LIMIT 100;

Be sure to replace some_condition with your desired condition.

Confirming deletion

By default, the DELETE statement in SQL CLI does not provide any confirmation message. To ensure that the deletion was successful, you can execute a SELECT statement before and after the deletion to verify the changes.

Conclusion

Using the DELETE statement in the SQL command-line interface, you can easily remove data from a database table. By understanding the syntax and using the appropriate conditions, you have the flexibility to delete specific rows or clear the entire table. Just remember to exercise caution and double-check your conditions before executing the DELETE statement.

For more information on SQL, you can check out the official documentation or refer to reputable SQL tutorial websites like W3Schools or SQLZoo.

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