How To Clear Mysql Database

Summary: in this tutorial, you will learn how to use the MySQL DELETE statement to delete data from a single table.

Introduction to MySQL `DELETE` statement

To delete data from a table, you use the MySQL DELETE statement. The following illustrates the syntax of the DELETE statement:

DELETE FROM table_name WHERE condition;

Code language: SQL (Structured Query Language) ( sql )

In this statement:

First, specify the table from which you delete data.
Second, use a condition to specify which rows to delete in the WHERE clause. The DELETE statement will delete rows that match the condition,

Notice that the WHERE clause is optional. If you omit the WHERE clause, the DELETE statement will delete all rows in the table.

Besides deleting data from a table, the DELETE statement returns the number of deleted rows.

To delete data from multiple tables using a single DELETE statement, you use the DELETE JOIN statement which will be covered in the next tutorial.

To delete all rows in a table without the need of knowing how many rows deleted, you should use theTRUNCATE TABLE statement to get better performance.

For a table that has a foreign key constraint, when you delete rows from the parent table, the rows in the child table will be deleted automatically by using the ON DELETE CASCADE option.

MySQL `DELETE` examples

We will use the employees table in the sample database for the demonstration.

Note that once you delete data, it is gone. Later, you will learn how to put the DELETE statement in a transaction so that you can roll it back.

Suppose you want to delete employees whose the officeNumber is 4, you use the DELETE statement with the WHERE clause as shown in the following query:

DELETE FROM employees WHERE officeCode = 4;

Code language: SQL (Structured Query Language) ( sql )

To delete all rows from the employees table, you use the DELETE statement without the WHERE clause as follows:

DELETE FROM employees;

Code language: SQL (Structured Query Language) ( sql )

All rows in the employees table deleted.

MySQL `DELETE` and `LIMIT` clause

If you want to limit the number of rows to delete, use the LIMIT clause as follows:

DELETE FROM table_table LIMIT row_count;

Code language: SQL (Structured Query Language) ( sql )

Note that the order of rows in a table is unspecified, therefore, when you use the LIMIT clause, you should always use the ORDER BY clause.

DELETE FROM table_name ORDER BY c1, c2, ... LIMIT row_count;

Code language: SQL (Structured Query Language) ( sql )

Consider the following customers table in the sample database:

For example, the following statement sorts customers by customer names alphabetically and deletes the first 10 customers:

DELETE FROM customers ORDER BY customerName LIMIT 10;

Code language: SQL (Structured Query Language) ( sql )

Similarly, the following DELETE statement selects customers in France, sorts them by credit limit in from low to high, and deletes the first 5 customers:

DELETE FROM customers WHERE country = 'France' ORDER BY creditLimit LIMIT 5;

Code language: SQL (Structured Query Language) ( sql )

In this tutorial, you have learned how to use the MySQL DELETE statement to delete data from a table.

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