SQL Joins with NOT IN displays incorrect data - sql

Question

I have 3 tables as below, and I need data where Expense.Expense_Code Should not be availalbe in Income.Income_Code.
Table: Base
+----+-----------+----------------+
| ID | Reference | Reference_Name |
+----+-----------+----------------+
| 1 | 10000 | AAAA |
| 2 | 10001 | BBBB |
| 3 | 10002 | CCCC |
+----+-----------+----------------+
Table: Expense
+-----+---------+--------------+----------------+
| EID | BASE_ID | Expense_Code | Expense_Amount |
+-----+---------+--------------+----------------+
| 1 | 1 | I0001 | 25 |
| 2 | 1 | I0002 | 50 |
| 3 | 2 | I0003 | 75 |
+-----+---------+--------------+----------------+
Table: Income
+------+---------+-------------+------------+
| I_ID | BASE_ID | Income_Code | Income_Amt |
+------+---------+-------------+------------+
| 1 | 1 | I0001 | 10 |
| 2 | 1 | I0002 | 20 |
| 3 | 1 | I0003 | 30 |
+------+---------+-------------+------------+
SELECT DISTINCT Base.Reference,Expense.Expense_Code
FROM Base
JOIN Expense ON Base.ID = Expense.BASE_ID
JOIN Income ON Base.ID = Income.BASE_ID
WHERE Expense.Expense_Code IN ('I0001','I0002')
AND Income.Income _CODE NOT IN ('I0001','I0002')
I expect no data be retured.
However I am getting the result as below:
+-----------+--------------+
| REFERENCE | Expense_Code |
+-----------+--------------+
| 10000 | I0001 |
| 10000 | I0002 |
+-----------+--------------+
For Base.Reference (10000), Expense.Expense_Code='I0001','I0002' the same expense_code is availalbe in Income table therefore I should not get any data.
Am I trying to do something wrong with the joins.
Thanks in advance for your help!

Answer 1

You are not joining EXPENSE and INCOME tables in your query at all. There needs to be a condition to join these tables in order to get desired result. You can also use NOT EXISTS clause. Prefer using NOT EXISTS over NOT IN as it performs better in case there are NULLS allowed in the columns that you're joining on.
SELECT * FROM BASE B
JOIN EXPENSE E ON B.ID=E.BASE_ID
WHERE E.EXPENSE_CODE NOT EXISTS (SELECT I.INCOME_CODE FROM INCOME I WHERE I.I_ID=E.EID)

Answer 2

When the first join is performed, you end with two lines possessing the ID 1, because the relationship between the tables is not 1o1, hence every line of the first table will have joined to it a line coming from the second table. Like so:
Output of the first join statement
Then, when the second part of your statement is executed, the DBMS finds two ID's 1 from the first joined table(BASE+EXPENSE) and 3 from the third table(INCOME).
Again since it's non a 1o1 relationship between tables, every row from the first joined table will have a joined line coming from the second table, like so: Output of the second join statement
Finally, when it reads your where clause and outputs what you see. I highlighted the excluded rows from the where clause
Output of where statement

Answer 3

...I need data where Expense.Expense_Code Should not be availalbe in Income.Income_Code
The following query will retrieve this data:
select b.*, e.*
from base b
join expense e on e.base_id = b.id
left join income i on i.base_id = e.base_id
and e.expense_code = i.income_code
where i.i_id is null
For reference the data script (slightly modified) is:
create table base (
id number(6),
reference number(6),
reference_name varchar2(10)
);
insert into base (id, reference, reference_name) values (1, 10000, 'AAAA');
insert into base (id, reference, reference_name) values (2, 10001, 'BBBB');
insert into base (id, reference, reference_name) values (3, 10002, 'CCCC');
create table expense (
eid number(6),
base_id number(6),
expense_code varchar2(10),
expense_amount number(6)
);
insert into expense (eid, base_id, expense_code, expense_amount) values (1, 1, 'I0001', 25);
insert into expense (eid, base_id, expense_code, expense_amount) values (2, 1, 'I0002', 50);
insert into expense (eid, base_id, expense_code, expense_amount) values (3, 1, 'I0003', 75);
insert into expense (eid, base_id, expense_code, expense_amount) values (4, 2, 'I0004', 101);
create table income (
i_id number(6),
base_id number(6),
income_code varchar2(10),
income_amt number(6)
);
insert into income (i_id, base_id, income_code, income_amt) values (1, 1, 'I0001', 10);
insert into income (i_id, base_id, income_code, income_amt) values (2, 1, 'I0002', 20);
insert into income (i_id, base_id, income_code, income_amt) values (3, 1, 'I0003', 30);
Result:
ID REFERENCE REFERENCE_NAME EID BASE_ID EXPENSE_CODE EXPENSE_AMOUNT
-- --------- -------------- --- ------- ------------ --------------
2 10,001 BBBB 4 2 I0004 101