Update

5.8. Update#

Sometimes we want to modify a record that already exists in our database.

For example, one of our customers might move to a new house. Then we would have to update their postcode.

To perform an UPDATE we need to SET new values and we also need to specify a criteria to identify records WHERE we will make our changes.

UPDATE table
SET attribute_1 = value_1, attribute_2 = value_2, ...
WHERE condition;

Example

We can update our customers table to change Wilson’s postcode.

../../_images/customers-wilson.png 
UPDATE customers
SET postcode = 6289
WHERE id = 5;

5.8.1. Primary Key#

You will have noticed that the condition we chose was id = 5, but equally, we could have used firstname = 'Wilson'.

The difference is that id is the primary key (it’s marked in the diagram by the underline). This means that no two records can have the same id. It is possible for multiple records to have 'Wilson' as the firstname, in which case we would be updating the postcodes of every record where firstname = 'Wilson'.

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