SQL UPDATE - SQL Tutorial
The SQL UPDATE general syntax looks like this:
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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 | 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:
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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:
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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 | 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 |