How to.. create new column with autofill data from other column?

I am struggling with adding column to my query with data from other column. 

Lets say ColumnA is [text1, , , ,text2, , , ,text3, , ,text4]
I need new ColumnB to copy values from Column1 looks like this [text1, text1, text1, text2, text2, text2, text3, text3, text4, text4....etc]
So logic will be check ColumnA, if there value copy to ColumnB, if there empty, copy previus copied value.