013 SQL DELETE

#Edu #SQL

The current page explains the SQL DELETE statement, which is used to remove existing records from a table in a database.

Key points:

Basic Syntax:
```
DELETE FROM table_name WHERE condition;
```
- The WHERE clause specifies which records to delete.
- Caution: If you omit the WHERE clause, all records in the table will be deleted!
Example:
To delete a specific customer from a "Customers" table:
```
DELETE FROM Customers WHERE CustomerName = 'Alfreds Futterkiste';
```
This removes only the row with CustomerName "Alfreds Futterkiste".
Delete All Rows:
To delete all data but keep the table structure:
```
DELETE FROM table_name;
```
Remove Entire Table:
To completely delete the table (structure and data), use:
```
DROP TABLE table_name;
```

The page also includes a quiz question to test your understanding:
"What is the purpose of the SQL DELETE statement?"
The correct answer is: To delete existing records from a table.[1]

SQL DELETE Statement

The SQL DELETE Statement

The DELETE statement is used to delete existing records in a table.

DELETE Syntax

DELETE FROM table_name WHERE condition;

Note: Be careful when deleting records in a table! Notice the WHERE clause in the DELETE statement. The WHERE clause specifies which record(s) should be deleted. If you omit the WHERE clause, all records in the table will be deleted!

Demo Database

Below is a selection from the Customers table used in the examples:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
1	Alfreds Futterkiste	Maria Anders	Obere Str. 57	Berlin	12209	Germany
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

SQL DELETE Example

The following SQL statement deletes the customer "Alfreds Futterkiste" from the "Customers" table:

DELETE FROM Customers WHERE CustomerName='Alfreds Futterkiste';

The "Customers" table will now look like this:

CustomerID	CustomerName	ContactName	Address	City	PostalCode	Country
2	Ana Trujillo Emparedados y helados	Ana Trujillo	Avda. de la Constitución 2222	México D.F.	05021	Mexico
3	Antonio Moreno Taquería	Antonio Moreno	Mataderos 2312	México D.F.	05023	Mexico
4	Around the Horn	Thomas Hardy	120 Hanover Sq.	London	WA1 1DP	UK
5	Berglunds snabbköp	Christina Berglund	Berguvsvägen 8	Luleå	S-958 22	Sweden

Delete All Records

It is possible to delete all rows in a table without deleting the table. This means that the table structure, attributes, and indexes will be intact:

DELETE FROM table_name;

The following SQL statement deletes all rows in the "Customers" table, without deleting the table:

DELETE FROM Customers;

Delete a Table

To delete the table completely, use the DROP TABLE statement:

Remove the Customers table:

DROP TABLE Customers;