PostgreSQL : comparing two sets of results does not work - postgresql

Question

I have a table that contains 3 columns of ids, clothes, shoes, customers and relates them.
I have a query that works fine :
select clothes, shoes from table where customers = 101 (all clothes and shoes of customer 101). This returns
clothes - shoes (SET A)
1 6
1 2
33 12
24 null
Another query that works fine :
select clothes ,shoes from table
where customers in
(select customers from table where clothes = 1 and customers <> 101 ) (all clothes and shoes of any other customer than 101, with specified clothes). This returns
shoes - clothes(SET B)
6 null
null 24
1 1
2 1
12 null
null 26
14 null
Now I want to get all clothes and shoes from SET A that are not in SET B.
So (example) select from SET A where NOT IN SET B. This should return just clothes 33, right?
I try to convert this to a working query :
select clothes, shoes from table where customers = 101
and
(clothes,shoes) not in
(
select clothes,shoes from
table where customers in
(select customers from table where clothes = 1 and customers <> 101 )
) ;
I tried different syntaxes, but the above looks more logic.
Problem is I never get clothes 33, just an empty set.
How do I fix this? What goes wrong?
Thanks
Edit , here is the contents of the table
id shoes customers clothes
1 1 1 1
2 1 4 1
3 1 5 1
4 2 2 2
5 2 3 1
6 1 3 1
44 2 101 1
46 6 101 1
49 12 101 33
51 13 102
52 101 24
59 107 51
60 107 24
62 23 108 51
63 23 108 2
93 124 25
95 6 125
98 127 25
100 3 128
103 24 131
104 25 132
105 102 28
106 10 102
107 23 133
108 4 26
109 6 4
110 4 24
111 12 4
112 14 4
116 102 48
117 102 24
118 102 25
119 102 26
120 102 29
122 134 31

Answer 1

The except clause in PostgreSQL works the way the minus operator does in Oracle. I think that will give you what you want.
I think notionally your query looks right, but I suspect those pesky nulls are impacting your results. Just like a null is not-NOT equal to 5 (it's nothing, therefore it's neither equal to nor not equal to anything), a null is also not-NOT "in" anything...
select clothes, shoes
from table1
where customers = 101
except
select clothes, shoes
from table1
where customers in (
select customers
from table1
where clothes = 1 and customers != 101
)

Answer 2

For PostgreSQL null is undefined value, so You must get rid of potential nulls in your result:
select id,clothes,shoes from t1 where customers = 101 -- or select id...
and (
clothes not in
(
select COALESCE(clothes,-1) from
t1 where customers in
(select customers from t1 where clothes = 1 and customers <> 101 )
)
OR
shoes not in
(
select COALESCE(shoes,-1) from
t1 where customers in
(select customers from t1 where clothes = 1 and customers <> 101 )
)
)
if You wanted unique pairs you would use:
select clothes, shoes from t1 where customers = 101
and
(clothes,shoes) not in
(
select coalesce(clothes,-1),coalesce(shoes,-1) from
t1 where customers in
(select customers from t1 where clothes = 1 and customers <> 101 )
) ;
You can't get "clothes 33" if You are selecting both clothes and shoes columns...
Also if u need to know exactly which column, clothes or shoes was unique to this customer, You might use this little "hack":
select id,clothes,-1 AS shoes from t1 where customers = 101
and
clothes not in
(
select COALESCE(clothes,-1) from
t1 where customers in
(select customers from t1 where clothes = 1 and customers <> 101)
)
UNION
select id,-1,shoes from t1 where customers = 101
and
shoes not in
(
select COALESCE(shoes,-1) from
t1 where customers in
(select customers from t1 where clothes = 1 and customers <> 101)
)
And Your result would be:
id=49, clothes=33, shoes=-1
(I assume that there aren't any clothes or shoes with id -1, You may put any exotic value here)
Cheers