Question

I have two tables:

• t1 (date d, name c(20), debit n(7), credit n(7))
• t2 (date d, name c(20), type c(25), obal n(7))

Here’s the sample data.

T1:

DATE        NAME        DEBIT   CREDIT
01.01.12    dad                 5000
01.01.12    mum                 6000
05.01.12    school      1000    
01.02.12    dad                 5000
01.02.12    mum                 6000
10.02.12    tuition     300 
10.02.12    snacks      100 
01.03.12    dad                 5000
01.03.12    mum                 6000
01.03.12    books       500 
02.03.12    rice        500 
02.03.12    vegetables  900 
03.03.12    snacks      100 
01.04.12    dad                 5000
01.04.12    mum                 6000
01.04.12    meat        200 
21.04.12    guest       800 

T2:

DATE        NAME        TYPE        OBAL
01.01.12    dr fee      medical     8000
01.01.12    medicine    medical     -10000
01.01.12    dad         income      400000
01.01.12    mum         income      450000
05.01.12    school      education   0
10.02.12    tuition     education   0
10.02.12    snacks      misc        0
01.03.12    books       education   0
02.03.12    rice        food        0
02.03.12    vegetables  food        0
01.04.12    meat        food        0
21.04.12    guest       misc        0

Sum of (obal + credit – debit) for each name grouped by type (t2) is expected. Query used and output obtained is:

SELECT 
    t2.type, obal + SUM(NVL(credit - debit, 0)) as bal 
FROM t2 
LEFT JOIN t1 ON t2.name = t1.name 
GROUP BY 
    t2.type, t2.obal

Results:

TYPE        BAL
education   -1800
food        -1600
income      420000
income      474000
medical     -10000
medical     8000
misc        -1000

My question is: why should the type income and medical comes twice in the query output in spite of GROUP BY clause being used? I’ve tried adding DISTINCT clause before the column t2.type and that too produces the same output! One thing I could observe is that the two records of type medical in table t2 has no records in t1 matching the same name and two records of type income has a non-zero obal in t2. Please help me to overcome this problem.

Answer 1

The problem is that you’re not grouping just by type, but also by obal.

Try:

select type,sum(bal) as bal
from(
  SELECT t2.type, obal + SUM(NVL(credit - debit, 0)) as bal FROM t2 LEFT JOIN t1 ;
  ON t2.name = t1.name GROUP BY t2.type, t2.obal
)a
group by type;