Hi @Anne-Marie Wood​ ,

I think it's more SQL general issue:

you are not comparing any value to `< 3`

it should be something like :

WHEN X < 3 THEN "under3"

    SELECT *, yrs_to_mat,
     CASE 
          WHEN X < 3 THEN "under3"
          WHEN X => 3 AND < 5 THEN "3to5"
          WHEN X => 5 AND < 10 THEN "5to10"
          WHEN X => 10 AND < 15 THEN "10to15"
          WHEN X => 15 THEN "over15"
          ELSE null END AS maturity_bucket
    FROM matyrs;