Problems with the CASE structure - response (1) by ulrich

Hm, not 100% sure but
row one is stored as '         ' in the char field and '' in the varchar field to my understanding.
Given your code the case results in Str1 which is '         ' and char length is 10.
for varchar the case results in '' and has a length of 0.
check type(TRIM(T1) )   -> this returns varchar(10) and explains why you get 

CHARACTER_LENGTH(T1) = 0