There are two tables with the type of column is char. when Using a 'like' predicate in a join condition will result in an incorrect result.
Because there is no 'like' operator that left operand and right operand are all bpchar.(bpchar ~~ bpchar), final the operator 'bpchar ~~ text' will be found form candidate set. so database do the cast from bpchar to text, The space at the end of the string was removed during the cast.
1、Following a example：
postgres=# create table t1(a char(6));
CREATE TABLE
postgres=# create table t2(a char(6));
CREATE TABLE
postgres=# insert into t1 values('aaa');
INSERT 0 1
postgres=# insert into t2 values('aaa');
INSERT 0 1
postgres=# select * from t1, t2 where t1.a=t2.a;
a | a
--------+--------
aaa | aaa
(1 row)
postgres=# select * from t1, t2 where t1.a like t2.a;
a | a
---+---
(0 rows)
postgres=#
2、The following example is a comparative:
postgres=# select 'aaa'::text like 'aaa'::text;
?column?
----------
t
(1 row)
postgres=# select 'aaa'::char(6) like 'aaa'::char(6);
?column?
----------
f
(1 row)
postgres=#