how does count work in sql query - qsqlquery

Question

I'm doing a exercise about SQL query and I came up with an error when it comes to SUM. I know what is does, but I somehow get an error...
select
client.LName, client.FName,
COUNT(b.Total)
from
ClientBank client
INNER JOIN
Bank b ON (client.ClientID = b.ClientID)
where
client.LName = 'name' AND client.FName = 'a';
But then I get this error...
Column 'ClientBank.LName' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
I have tried to do a Group BY, don't really know how to use it well.. Any help would be great!

Answer 1

You have not given the structure of the ClientBank and Bank tables. I am taking that you inserted records something like this:
INSERT INTO `ClientBank`
(`ClientID`, `FName`, `Lname`)
VALUES
(1, 'Abraham', 'Backman'),
(2, 'Carl', 'Dacosta'),
(3, 'Erwin', 'Fabio'),
(4, 'Gabriel', 'Haddon');
INSERT INTO `Bank`
(`DepositID`, `ClientID`, `Deposit`)
VALUES
(1, 1, 100),
(2, 2, 200),
(3, 3, 300),
(4, 4, 400),
(5, 2, 500),
(6, 3, 600);
You can get the total of deposit for each client with this:
SELECT
client.LName, client.FName, SUM(b.Deposit) as Total
FROM
ClientBank client
INNER JOIN
Bank b ON (client.ClientID = b.ClientID)
GROUP By
client.LName, client.FName;
If you want only for a particular client (filtering using their name than Client Id):
SELECT
client.LName, client.FName, SUM(b.Deposit) as Total
FROM
ClientBank client
INNER JOIN
Bank b ON (client.ClientID = b.ClientID)
WHERE
client.LName = 'Fabio' AND client.FName = 'Erwin'
GROUP By
client.LName, client.FName;