SQL - UPDATE

The SQL UPDATE general syntax looks like this:

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

The UPDATE clause changes the data in already existing database row(s) and usually we need to add a conditional WHERE clause to our 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 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 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 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