Using MySQL DELETE to Remove Data from Tables

MySQL DELETE statement to remove data from one ore more database tables.

To remove data from a table, you use the MySQL DELETE statement. The MySQL DELETE statement allows you to remove records from not only one table but also multiple tables using a single DELETE statement.

MySQL delete from one table

To remove data from a single table, you use the following DELETE statement:

1 2	DELETE FROM table   [WHERE conditions] [ORDER BY ...] [LIMIT rows]

Followed the DELETE FROM clause is the table name that you want to delete records.

The WHERE clause specifies which rows you want to delete. If a record meets the WHERE condition, it is deleted permanently from the table. If you omit the WHERE clause, all records in the table are deleted.

The DELETE statement returns the number of rows deleted specified by the ROW_COUNT() function.

Notice that the ROW_COUNT() function returns the number of rows inserted, updated or deleted by the last INSERT, UPDATE or DELETE statement

MySQL delete from a table examples

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

1 2	DELETE FROM employees WHERE officeCode = 4

To delete all employee records from the employees table, you use the DELETE statement without theWHERE clause as follows:

1	DELETE FROM employees

All employee records in the employees table were deleted.

MySQL delete from multiple tables

To delete records from multiple tables, you use one of the following DELETE statements:

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DELETE table_1, table_2,... FROM table-refs   [WHERE conditions]   DELETE FROM table_1, table_2,... USING table-refs [WHERE conditions]

Let’s examine each statement in greater detail:

• Both DELETE statements delete records from multiple tables i.e., table_1, table_2,… specified after the DELETE keyword.
• The first DELETE statement uses the FROM clause while the second one use the USING clause.
• The WHERE clause is used to determine which record to be deleted.
• Both statements return the number of rows deleted from the multiple tables.

MySQL delete from multiple tables example

Let’s take a look at the offices and employees tables in the MySQL sample database.

Suppose one office is closed and you want to remove all employee records in the employees table associated with that office and also the office itself in the offices table, you can use the second form of the MySQL DELETE statement

The following query removes the office record with the code is 1 in the offices table and also all employee records associated with the office 1 in the employees table:

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DELETE employees,    offices FROM employees, offices WHERE employees.officeCode = offices.officeCode  AND       offices.officeCode = 1

You can verify the changes by using the following SELECT statements to query data from both employeestable and offices table.

1 2 3 4 5

SELECT * FROM employees WHERE officeCode = 1;   SELECT * FROM offices WHERE officeCode = 1;

You can achieve the same effect by using the second form of the MySQL DELETE statement as follows:

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DELETE FROM employees, offices USING employees, offices WHERE employees.officeCode = offices.officeCode  AND       offices.officeCode = 1