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SQL Anywhere 11.0.1 » SQL Anywhere Server - SQL Usage » Querying and Modifying Data » Adding, changing, and deleting data

 

Deleting data using DELETE

Simple DELETE statements have the following form:

DELETE [ FROM ] table-name 
WHERE column-name = expression

You can also use a more complex form, as follows

DELETE [ FROM ] table-name 
FROM table-list 
WHERE search-condition
The WHERE clause

Use the WHERE clause to specify which rows to remove. If no WHERE clause appears, the DELETE statement remove all rows in the table.

The FROM clause

The FROM clause in the second position of a DELETE statement is a special feature allowing you to select data from a table or tables and delete corresponding data from the first-named table. The rows you select in the FROM clause specify the conditions for the delete. See DELETE statement.

Example

This example uses the SQL Anywhere sample database. To execute the statements in the example, you should set the option wait_for_commit to On. The following statement does this for the current connection only:

SET TEMPORARY OPTION wait_for_commit = 'On';

This allows you to delete rows even if they contain primary keys referenced by a foreign key, but does not permit a COMMIT unless the corresponding foreign key is deleted also.

The following view displays products and the value of that product that has been sold:

CREATE VIEW ProductPopularity as
SELECT  Products.ID,
   SUM( Products.UnitPrice * SalesOrderItems.Quantity ) 
   AS "Value Sold"
FROM  Products JOIN SalesOrderItems
ON Products.ID = SalesOrderItems.ProductID
GROUP BY Products.ID;

Using this view, you can delete those products which have sold less than $20,000 from the Products table.

DELETE
FROM Products
FROM Products NATURAL JOIN ProductPopularity
WHERE "Value Sold" < 20000;

Cancel these changes to the database by entering a ROLLBACK statement:

ROLLBACK;
Tip

You can also delete rows from database tables from the Interactive SQL result set. See Editing result sets in Interactive SQL.


Deleting all rows from a table