Updating EMPTY cells

[Jonny]

I need to update column 'customer' in table 'db' with a name of a customer.
Currently this column is empty from data.

I do following , but it doesn't work.

UPDATE db SET Customer = 'Microsoft'
WHERE Customer='';

Where is the problem.

 

[Brianwarnock]

WHERE Customer Is Null;

Brian

 

[Jonny]

Thank you