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UPDATE

The UPDATE statement allows you to modify existing data in a database. There are three clauses to the basic UPDATE statement:

 

UPDATE tablename

SET field1=value1, field2=value2...

WHERE condition1, condition2

The WHERE clause is optional, but should not be omitted unless you deliberately intend to update all rows in a table. The WHERE clause determines which rows in the table should be updated, while the SET clause specifies which columns should be updated and the values to set them to.

The UPDATE clause specifies the table to be updated. Only one table can be updated at a time. The following example demonstrates how to use the UPDATE statement:

Example:

UPDATE tblAddressBook

SET

Address = '23 London Street, London',

PostCode = 'L99 9ZZ'

PhoneNumber = '0976 543 210'

WHERE

Name = 'Stephen Smith'

In this example, Stephen Smith's address and phone number are updated. If the WHERE clause had been omitted, then all rows in the table would have had their address and phone number updated to the above values.

 

In the SET clause, the new values for the fields can also be specified by looking up fields from other tables, or from an expression. For example, to update the age column the following expression can be used in the SET clause.

Example:

UPDATE tblAddressBook

SET

Age = Age + 1

WHERE

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