I have following table:

```
CREATE table table1 (id int , cd date, ct TIME, co text)

INSERT INTO table1 
VALUES (0, '1/1/2018', '12:00:00', 'B'), 
        (1, '1/1/2018', '12:30:00', 'BC'), 
        (2, '1/12/2018', '12:00:00', 'B'), 
        (3, '1/22/2018', '12:00:00', 'BC')

```

I need to combine "co" column when values of "cd" and "ct" columns are the same for 'B' AND 'BC' or only values of "ct" are different and display values of record 'B' for 'B-BC'. 
for the above table1 records I need following result:

```
"id"    "cd"    "ct"    "co"
"0" "1/1/2018"  "12:00:00 PM"   "B-BC"
"2" "1/12/2018" "12:00:00 PM"   "B"
"3" "1/22/2018" "12:00:00 PM"   "BC"

```

What is the most effective way to do that in postgresql 8.4?