Question

I need ideas to optimize this query:

SELECT U.Id
    , U.Name
    , SUM(P.Credit) AS CreditAmount
    , SUM(P.Debit) AS DebitAmount
    FROM users U
    LEFT JOIN payments P ON P.UserId = U.Id
    WHERE U.StatusId = 1 /* Active Users Only */
    GROUP BY U.Id

Some information about the tables:

1. users table: 10,000+ records
2. payments table: 2,000,000+ records, indexed on UserId column

The query takes up to 2 minutes. By investigating the query, I found out that the SUM function is the reason why the query is slow. Tried executing the query without the SUM takes less than 2 seconds.

Is there any room to improve this query? Thanks

EDIT 1

This is what I got when using the EXPLAIN:

id  select_type table   type    possible_keys   key     key_len     ref             rows    Extra
1   SIMPLE      U       ALL                                                         8304    Using where; Using temporary; Using filesort
1   SIMPLE      P       ref     UserId          UserId  5           Database.U.Id   361     ""

The index payments.UserId is being used in the query. Any thoughts on this?

EDIT 2
Table Information:

users   "CREATE TABLE `users` (
  `Id` int(11) NOT NULL auto_increment,
  `StatusId` int(11) default NULL,
  `Name` varchar(60) default NULL,
  `TimeZone` varchar(100) default NULL,
  PRIMARY KEY  (`Id`),
  KEY `StatusId` (`StatusId`),
  CONSTRAINT `FK_User_Status` FOREIGN KEY (`StatusId`) REFERENCES `userStatus` (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8"

payments    "CREATE TABLE `payments` (
  `Id` int(11) NOT NULL auto_increment,
  `UserId` int(11) default NULL,  
  `Description` varchar(200) default NULL,
  `Debit` decimal(11,2) default NULL,
  `Credit` decimal(11,2) default NULL,
  `Date` datetime default NULL,
  PRIMARY KEY  (`Id`),
  KEY `UserId` (`UserId`),
  CONSTRAINT `FK_Payment_User` FOREIGN KEY (`UserId`) REFERENCES `users` (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8"

Answer 1

According this link, I can’t speed up the SUM function. The main issue here is that I’m selecting a huge number of records.

I thought of redesigning the users table, adding a new column like TotalPayment which will hold the total credit minus debit amount from the payments table. I know it disobeys the database normalization rules, but I guess this redesign is for saving performance.

Thanks a lot for your help guys.