Merging 2 columns

Hi there!

I want to combine 2 columns of 1 single table, e.g. (hope it makes sense)

My table
ID - column1 - column2 - column3
1 - andre - peter - jack
2 - peter - andre - andre
3 - jack - jack - peter

And I only want to select

columname
andre
peter
jack
peter
andre
andre
jack
jack
peter

select column1 from t
union all
select column2 from t
union all
select column3 from t