Error while using group by - sql

Question

In table A I have the dates, and in B I have the order numbers.
In both tables I have a common field called order Id.
I just have a simple goal to fetch the number of orders on each date[ as in 1st, 2nd ..]
Here is what I have tried as I dont want to use joins or views.
select
A.date_of_order,
count(B.order_number)
from A, B
where A.order_id=B.order_id;
group by A.date_of_order
I am getting the following error. Probably making some trivial error. Thanks in advance
Update:
After taking into consideration Dmitri and rafa s suggestions, I get the table as:
23-FEB-14 1
23-FEB-14 1
23-FEB-14 2
23-FEB-14 2
23-FEB-14 2
07-MAR-14 2
07-MAR-14 4
07-MAR-14 1
07-MAR-14 5
02-MAR-14 1
02-MAR-14 1
As I said my requirement is very simple, just get it as
23-Feb-14 10[i.e. all the orders placed on this date]
07-Mar-14 13
02-mar-14 2

Answer 1

WHERE should be put before GROUP BY:
select A.date_of_order,
count(B.order_number)
from A, B
where A.order_id = B.order_id -- <- possible, but join will be better here
group by A.date_of_order
If you want a condition after GROUP BY you should use HAVING
select A.date_of_order,
count(B.order_number)
from A, B
where A.order_id = B.order_id
group by A.date_of_order
having count(B.order_number) < 3 -- having demo

Answer 2

The WHERE clause must to be before of the GROUP BY clause.
Use TRUNC(date) to get rid of the time so the GROUP BY will work as expected.
SELECT TRUNC(A.date_of_order), COUNT(B.order_number)
FROM A, B
WHERE A.order_id=B.order_id
GROUP BY TRUNC(A.date_of_order)
Anyway it is recommended to use the ANSI-standard SQL JOIN clause instead.
SELECT TRUNC(A.date_of_order), COUNT(B.order_number)
FROM A INNER JOIN B ON A.order_id = B.order_id
-- (WHERE conditions here)
GROUP BY TRUNC(A.date_of_order)
-- (HAVING conditions here)

Answer 3

The possible reasons could be that
1) Dates have timestamp, in that case following query would be helpful:
select
trunc(A.date_of_order),
count(B.order_number)
from A, B
where A.order_id=B.order_id
group by trunc(A.date_of_order);
2) Since in your sample data, you already have count against the dates, you need to take sum instead of count for your query
select
A.date_of_order,
sum(B.order_number)
from A, B
where A.order_id=B.order_id
group by A.date_of_order;
3) Or could be both, in that case you can try
select
trunc(A.date_of_order),
sum(B.order_number)
from A, B
where A.order_id=B.order_id
group by trunc(A.date_of_order);

Answer 4

I don't see why you need to join to that other table at all. Try just running:
select date_of_order, count(order_id) from tbl_a group by date_of_order
Your question states that table A contains rows for each order ID and date, and all you want to do is count the number of orders by date.