SQL UPDATE

The SQL UPDATE general syntax looks like this:


UPDATE Table1
SET Column1 = Value1, Column2 = Value2
WHERE Some_Column = Some_Value

The SQL UPDATE clause changes the data in already existing database row(s) and usually we need to add a conditional SQL WHERE clause to our SQL UPDATE statement in order to specify which row(s) we intend to update.

If we want to update the Mr. Steven Goldfish's date of birth to '5/10/1974' in our Customers database table

FirstName LastName Email DOB Phone
John Smith John.Smith@yahoo.com 2/4/1968 626 222-2222
Steven Goldfish goldfish@fishhere.net 4/4/1974 323 455-4545
Paula Brown pb@herowndomain.org 5/24/1978 416 323-3232
James Smith jim@supergig.co.uk 20/10/1980 416 323-8888

we need the following SQL UPDATE statement:


UPDATE Customers
SET DOB = '5/10/1974'
WHERE LastName = 'Goldfish' AND FirstName = 'Steven'

If we don’t specify a WHERE clause in the SQL expression above, all customers' DOB will be updated to '5/10/1974', so be careful with the SQL UPDATE command usage.

We can update several database table rows at once, by using the SQL WHERE clause in our UPDATE statement. For example if we want to change the phone number for all customers with last name Smith (we have 2 in our example Customers table), we need to use the following SQL UPDATE statement:


UPDATE Customers
SET Phone = '626 555-5555'
WHERE LastName = 'Smith'

After the execution of the UPDATE SQL expression above, the Customers table will look as follows:

FirstName LastName Email DOB Phone
John Smith John.Smith@yahoo.com 2/4/1968 626 555-5555
Steven Goldfish goldfish@fishhere.net 4/4/1974 323 455-4545
Paula Brown pb@herowndomain.org 5/24/1978 416 323-3232
James Smith jim@supergig.co.uk 20/10/1980 626 555-5555