Bad Performance or Bad Query ?

I have three tables like this:

receipts
±-----------±------±-----±-----------±----------+| customerId | recID | plan | recDate | processed |±-----------±------±-----±-----------±----------+| 9742 | 900 | 1 | 1178726955 | 0 || 2188 | 899 | 1 | 1178670358 | 0 || 2657 | 898 | 1 | 1178639090 | 0 || 9699 | 897 | 1 | 1178627303 | 0 || 1247 | 896 | 1 | 1178570875 | 0 |±-----------±------±-----±-----------±----------+

customer
±------------------------------±---------±----------+| Email | LastName | FirstName |±------------------------------±---------±----------+| user1@domain.com | lname | fname || user2@domain.com | lname | fname || user3@domain.com | lname | fname || user4@domain.com | lname | fname || user5@domain.com | lname | fname |±------------------------------±---------±----------+

user
±---------±-------------±------------+| Approved | UserUpgraded | UpgradeDate |±---------±-------------±------------+| 1 | 1 | 1176134955 || 1 | 1 | 1176078358 || 1 | 1 | 1176047090 || 1 | 1 | 1176035303 || 1 | 1 | 1175978875 |±---------±-------------±------------+

each table is actually much bigger than that, over 10,000 entries … now i need to get all three table’s info at once … since there is no index associated with any of those (poorly designed … not by me) i am forced to use the WHERE clause.

now this is where i get messed up … this query:

SELECT DISTINCT receipts.customerId, receipts.recID, receipts.plan, receipts.recDate, receipts.processed, customer.Email, customer.LastName, customer.FirstNameFROM receipts, customerWHERE receipts.customerId = customer.CustomerIdGROUP BY receipts.customerIdORDER BY receipts.recID DESCLIMIT 5;

produces the following result:

±-----------±------±-----±-----------±----------±------------------------------±---------±----------+| customerId | recID | plan | recDate | processed | Email | LastName | FirstName |±-----------±------±-----±-----------±----------±------------------------------±---------±----------+| 9742 | 900 | 1 | 1178726955 | 0 | user1@domain.com | lname | fname || 2188 | 899 | 1 | 1178670358 | 0 | user2@domain.com | lname | fname || 2657 | 898 | 1 | 1178639090 | 0 | user3@domain.com | lname | fname || 9699 | 897 | 1 | 1178627303 | 0 | user4@domain.com | lname | fname || 1247 | 896 | 1 | 1178570875 | 0 | user5@domain.com | lname | fname |±-----------±------±-----±-----------±----------±------------------------------±---------±----------+5 rows in set (0.01 sec)

which is fine … but as soon as i add my third and last table into play … the query takes about 2 mins to process and uses 50+% CPU … this is the query i try to run:

SELECT DISTINCT receipts.customerId, receipts.recID, receipts.plan, receipts.recDate, receipts.processed, customer.Email, customer.LastName, customer.FirstName, user.Approved, user.UserUpgraded, user.UpgradeDate FROM receipts, customer, user WHERE receipts.customerId=customer.CustomerId AND customer.Email=user.UserEmail GROUP BY receipts.customerId ORDER BY receipts.recID DESC;LIMIT 5;

am i doing something wrong ? any help would be appreciated

p.s. the reason im doing distinct and group by customer id from the receipts table is because there are multiple receipts for each customer … and i want to get the latest one!

p.s.s. the user table also has an email column, thats how the user and customer tables are linked …

oh and i forgot … system info:

Processor: 4 x Xeon 3 Ghz
OS: RedHat Linux
Memory : 2 GB
Mysql: 4.1.22-standard

Show me result for EXLAIN SELECT for both queries.

Example

EXPLAIN SELECT
DISTINCT receipts.customerId,
receipts.recID,
receipts.plan,
receipts.recDate,
receipts.processed,
customer.Email,
customer.LastName,
customer.FirstName,
user.Approved,
user.UserUpgraded,
user.UpgradeDate
FROM
receipts,
customer,
user
WHERE
receipts.customerId=customer.CustomerId AND
customer.Email=user.UserEmail
GROUP BY
receipts.customerId
ORDER BY
receipts.recID DESC;
LIMIT
5;