QUERY: SELECT 'c'::char = 'c'::char AS true;
true
----
t   
(1 row)

QUERY: CREATE TABLE CHAR_TBL(f1 char);
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('a');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('A');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('1');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES (2);
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('3');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('cd');
QUERY: SELECT '' AS seven, CHAR_TBL.*;
seven|f1
-----+--
     |a 
     |A 
     |1 
     |2 
     |3 
     |  
     |c 
(7 rows)

QUERY: SELECT '' AS six, c.*
   FROM CHAR_TBL c
   WHERE c.f1 <> 'a';
six|f1
---+--
   |A 
   |1 
   |2 
   |3 
   |  
   |c 
(6 rows)

QUERY: SELECT '' AS one, c.*
   FROM CHAR_TBL c
   WHERE c.f1 = 'a';
one|f1
---+--
   |a 
(1 row)

QUERY: SELECT '' AS five, c.*
   FROM CHAR_TBL c
   WHERE c.f1 < 'a';
five|f1
----+--
    |A 
    |1 
    |2 
    |3 
    |  
(5 rows)

QUERY: SELECT '' AS six, c.*
   FROM CHAR_TBL c
   WHERE c.f1 <= 'a';
six|f1
---+--
   |a 
   |A 
   |1 
   |2 
   |3 
   |  
(6 rows)

QUERY: SELECT '' AS one, c.*
   FROM CHAR_TBL c
   WHERE c.f1 > 'a';
one|f1
---+--
   |c 
(1 row)

QUERY: SELECT '' AS two, c.*
   FROM CHAR_TBL c
   WHERE c.f1 >= 'a';
two|f1
---+--
   |a 
   |c 
(2 rows)

QUERY: DROP TABLE CHAR_TBL;
QUERY: CREATE TABLE CHAR_TBL(f1 char(4));
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('a');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('ab');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('abcd');
QUERY: INSERT INTO CHAR_TBL (f1) VALUES ('abcde');
QUERY: SELECT '' AS four, CHAR_TBL.*;
four|f1  
----+----
    |a   
    |ab  
    |abcd
    |abcd
(4 rows)