Question

I have two tables on MySQL, with this structure:

Users:
id | name

Accounts:
id | userid | amount

I need a query to get the total accounts for each user, with the user name in the result too. Is there a way to achieve this? I’ve tried subqueries in the from clause, and I don’t know how to use a join to achieve this, but I have my doubts if that may be the solution… Any ideas?

Here’s sample data and an example output I’m pretending to get:

Users
1 | 'John'
2 | 'Peter'

Accounts
1 | 1 | 1000
2 | 1 | 2000
3 | 2 | 1500

query:
'John'  | 2  <- there are 2 accounts for user 'John'
'Peter' | 1  <- there is only 1 account for user 'Peter'

Also, what if I like to have more summary data on my results? say… the total amounts. For example:

another query:
'John'  | 2 | 3000 <- 2 accounts for John, which sums 3000
'Peter' | 1 | 1500 <- 1 account for Peter, which sums 1500

Answer 1

Here’s a query to get the user’s name and the count of their accounts:

SELECT u.name, COUNT(a.id) AS numAccounts
FROM Users u
LEFT JOIN Accounts a ON u.id=a.userid
GROUP BY u.id;

To get a sum of the amount column, you can do something like:

SELECT u.name, COUNT(a.id) AS numAccounts, SUM(u.amount) AS totalAmount
FROM Users u
LEFT JOIN Accounts a ON u.id=a.userid
GROUP BY u.id;