> case when 1 = 1 then 'a' else 'ab' end || 'c'

case acts as decode, so it also returns 'a c'.

...but consider this ugly piece (sometimes not even trim is a solution
as you see below, when I need to specify padding):

decode(a.allow_multivalue, 1, 'LIST ', cast('' as varchar(1)))||
decode(a.is_boolean, 1, '*',
decode(a.is_scalar, 1, 'Scalar',
trim(decode(a.is_blob, 1, 'Text(Large)', 'Text')))||
decode(a.is_lang_neutral, 1, '', ' ML'))