D UNPIVOT (select 42 as col1, 'woot' as col2)
          on col1, col2;
Error: Binder Error: Cannot unpivot columns of types INTEGER and VARCHAR - an explicit cast is required
Full list: col1 INTEGER, col2 VARCHAR
                         ^

D unpivot (select 42 as col1, 'woot' as col2)
          on col1::VARCHAR, col2;
┌─────────┬─────────┐
│  name   │  value  │
│ varchar │ varchar │
├─────────┼─────────┤
│ col1    │ 42      │
│ col2    │ woot    │
└─────────┴─────────┘

D unpivot (select 42 as col1, 'woot' as col2)
          on col1+col2;
Error: Binder Error: UNPIVOT clause must contain exactly one column - expression "(col1 + col2)" contains multiple (col1, col2)
LINE 2:         on col1+col2;
                       ^

D unpivot (select 42 as col1, 'woot' as col2)
          on columns(*)::VARCHAR;
┌─────────┬─────────┐
│  name   │  value  │
│ varchar │ varchar │
├─────────┼─────────┤
│ col1    │ 42      │
│ col2    │ woot    │
└─────────┴─────────┘