SQL UPDATE Statement

From http://www.w3schools.com (Copyright Refsnes Data)

# SQL UPDATE Statement

The UPDATE statement is used to update records in a table.

## The UPDATE Statement

The UPDATE statement is used to update existing records in a table.

### SQL UPDATE Syntax

    UPDATE table_name
    SET column1=value, column2=value2,...
    WHERE some_column=some_value

Note: Notice the WHERE clause in the UPDATE syntax. The WHERE clause specifies which record or records that should be updated. If you omit the WHERE clause, all records will be updated!

## SQL UPDATE Example

The "Persons" table:

P_Id | LastName | FirstName | Address | City
--- | --- | --- | --- | ---
1 | Hansen | Ola | Timoteivn 10 | Sandnes
2 | Svendson | Tove | Borgvn 23 | Sandnes
3 | Pettersen | Kari | Storgt 20 | Stavanger
4 | Nilsen | Johan | Bakken 2 | Stavanger
5 | Tjessem | Jakob |  |

Now we want to update the person "Tjessem, Jakob" in the "Persons" table.

We use the following SQL statement:

    UPDATE Persons
    SET Address='Nissestien 67', City='Sandnes'
    WHERE LastName='Tjessem' AND FirstName='Jakob'

The "Persons" table will now look like this:

P_Id | LastName | FirstName | Address | City
--- | --- | --- | --- | ---
1 | Hansen | Ola | Timoteivn 10 | Sandnes
2 | Svendson | Tove | Borgvn 23 | Sandnes
3 | Pettersen | Kari | Storgt 20 | Stavanger
4 | Nilsen | Johan | Bakken 2 | Stavanger
5 | Tjessem | Jakob | Nissestien 67 | Sandnes

## SQL UPDATE Warning

Be careful when updating records. If we had omitted the WHERE clause in the example above, like this:

    UPDATE Persons
    SET Address='Nissestien 67', City='Sandnes'

The "Persons" table would have looked like this:

P_Id | LastName | FirstName | Address | City
--- | --- | --- | --- | ---
1 | Hansen | Ola | Nissestien 67 | Sandnes
2 | Svendson | Tove | Nissestien 67 | Sandnes
3 | Pettersen | Kari | Nissestien 67 | Sandnes
4 | Nilsen | Johan | Nissestien 67 | Sandnes
5 | Tjessem | Jakob | Nissestien 67 | Sandnes

From http://www.w3schools.com (Copyright Refsnes Data)