The following scenario needs to work:
create table vc (v varchar(10));
insert into vc select 'a';
ERROR: AnalysisException: Possible loss of precision for target table 'default.vc'.
Expression ''a'' (type: STRING) would need to be cast to VARCHAR(10) for column 'v'
Use explicit casts.
Query: insert into vc select cast('a' as varchar(10))
Inserted 1 row(s) in 0.32s