I don't have the right answer in SQL - sql

Question

List the project numbers (PR_NO) for projects that have only received parts that are stored in (P_CITY) the same city as the project (show output of the query).
Table: EMP
Primary Key: E_NO
E_NO E_NAME E_RATE E_DEPT
1 A $400.00
2 B $200.00 1
3 C $150.00 2
4 D $150.00 3
5 E $120.00 1
6 F $100.00 1
7 G $100.00 2
8 H $50.00 2
9 I $50.00 3
10 J $50.00 3
11 K $150.00 3
Table: PART
Primary Key: P_NO
P_NO P_NAME P_CITY
1 P1 NY
2 P2 NY
3 P3 LA
4 P4 SF
5 P5 LA
6 P6 NY
Table: PROJECT
Primary Key: PR_NO
PR_NO PR_MGR PR_DEPT PR_LOC
1 2 1 NY
2 3 2 LA
3 2 1 NY
Table: SUPPLIER
Primary Key: S_NO
S_NO S_NAME S_LOC
1 S1 NY
2 S2 NY
3 S3 LA
Table: SUPPLY
Primary Key: P_NO + PR_NO + S_NO
Foreign Key: P_NO references PART
Foreign Key: PR_NO references PROJECT
Foreign Key: S_NO references SUPPLIER
P_NO PR_NO S_NO QTY
1 1 1 111
1 1 2 112
1 1 3 113
1 2 1 121
1 2 2 122
1 2 3 123
1 3 1 131
1 3 2 132
1 3 3 133
2 1 1 211
3 1 1 311
4 1 1 411
5 1 1 511
6 1 1 611
Table: WORK
Primary Key: E_NO + PR_NO
Foreign Key: E_NO references EMP
Foreign Key: PR_NO references PROJECT
E_NO PR_NO HRS
2 1 10
3 2 20
5 1 20
5 2 20
5 3 20
6 1 10
6 2 10
select distinct P.PR_NO
from PROJECT P, PART PA
where PA.P_CITY = P.PR_LOC;
The right answer question should be :
PR_NO
3
This is the error:
PR_NO
1
3
2

Answer 1

In order to achieve this task, you also need to use Supply table as follows:
select s.pr_no
from supply s
inner join part p
on p.p_no = s.p_no
group by s.pr_no
having max(p.p_city) = min(p.p_city)
and min(p.p_city) = (select pr_loc
from project
where pr_no = s.pr_no
)

Answer 2

I tested this query with your example data and it returns project #3 as expected:
SELECT DISTINCT S.PR_NO
FROM
SUPPLY S
INNER JOIN PROJECT PR
ON S.PR_NO = PR.PR_NO
INNER JOIN PART P
ON S.P_NO = P.P_NO
WHERE
PR.PR_LOC = P.P_CITY AND
NOT S.PR_NO IN
(
SELECT S2.PR_NO
FROM
SUPPLY S2
INNER JOIN PROJECT PR2
ON S2.PR_NO = PR2.PR_NO
INNER JOIN PART P2
ON S2.P_NO = P2.P_NO
WHERE PR2.PR_LOC <> P2.P_CITY
)
The SUPPLY table creates the link between PART and PROJECT. The main query looks for parts that are stored in the same city as the project. The sub-select in the where clause looks almost the same, except that it looks for parts stored in a different city. Projects with such cities are excluded with NOT S.PR_NO IN (...).

Answer 3

The main issue in your query is that you should correctly join the 2 tables PROJECT and PART before filtering; so in this case you should use the table SUPPLY.
SELECT DISTINCT S.PR_NO
FROM SUPPLY S
INNER JOIN PROJECT PR
ON S.PR_NO = PR.PR_NO
INNER JOIN PART P
ON S.P_NO = P.P_NO
WHERE PR.PR_LOC = P.P_CITY
AND S.PR_NO NOT IN ( SELECT DISTINCT S.PR_NO
FROM SUPPLY S
INNER JOIN PROJECT PR
ON S.PR_NO = PR.PR_NO
INNER JOIN PART P
ON S.P_NO = P.P_NO
WHERE PR.PR_LOC <> P.P_CITY );
Hope this helps!