mysql change all values in a column

Question

I want to change all values in the tablecolumn \"Quellendatum\".

When the row-value is 2005-06-20 then it should be replaced with 2012-06-20. When the row-value is N

Answer 1

it should be :

UPDATE tablename 
SET Quellendatum = '2012-06-20' 
WHERE Quellendatum = '2005-06-20'