SQL CASE statement to modify column

Hi I have a question. Does the CASE statement ALWAYS result in creating a new column ( in the example, ‘Mood)’? Or can be used to modify the values of an existing column? If so what would be the structure of the statement?

Does someone know? - Thank you

Okay if you want to update values in a column .then you need to use UPDATE.you can look it up.
If you want to modify as in change the datatype of that column the you need ALTER.
Not sure where you are getting the definition of CASE but it just goes through conditions an returns a value of the true condition