Table: christmas_songs
Columns: rank
song_title
composer_s
performer_s
year

Question: Who sang the song composed by Mariah Carey and Walter Afanasieff?
SQL: SELECT "performer_s" FROM christmas_songs WHERE "composer_s" = 'mariah carey and walter afanasieff'

Question: How many years was Louis Armstrong performing?
SQL: SELECT COUNT("year") FROM christmas_songs WHERE "performer_s" = 'louis armstrong'