Question

I’ve got the SQL query below:

SELECT message, sent_date, user_id
FROM messages
LEFT JOIN numbers ON messages.from_id = numbers.id

It returns all the rows (about 4000) in the messages table with additional columns coming from the numbers table. So far, this is what I would expect.

Now I left join this sub-query to another table, again using a left join:

SELECT message, sent_date
FROM (
    SELECT message, sent_date, user_id
    FROM messages
    LEFT JOIN numbers ON messages.from_id = numbers.id
) AS table1
LEFT JOIN users ON table1.user_id = users.id

However, it only returns about 200 rows so many are missing. Since this is a left join I would expect all the rows from table1 to be in the result. Can anybody see what the issue is?

Edit:

So for information here are the 3 relevant tables (with irrelevant columns removed):

CREATE TABLE IF NOT EXISTS `messages` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `message` text CHARACTER SET utf8 NOT NULL,
  `from_id` int(11) DEFAULT NULL,
  `sent_date` datetime NOT NULL,
  PRIMARY KEY (`id`),
  KEY `from_id` (`from_id`),
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=101553 ;

CREATE TABLE IF NOT EXISTS `numbers` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `user_id` int(11) DEFAULT NULL,
  `number` varchar(32) NOT NULL,
  PRIMARY KEY (`id`),
  KEY `user_id` (`user_id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=6408 ;

CREATE TABLE IF NOT EXISTS `users` (
  `id` int(11) NOT NULL AUTO_INCREMENT,
  `name` varchar(256) CHARACTER SET utf8 DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB  DEFAULT CHARSET=latin1 AUTO_INCREMENT=2395 ;

Answer 1

You can try alternative method to debug the issue:

CREATE TEMPORARY table tmp1 AS SELECT message, sent_date, user_id
                               FROM messages
                                    LEFT JOIN numbers 
                                        ON messages. from_id = numbers.id;

and then see whether this query works.

 SELECT message, sent_date
 FROM tmp1 table1
      LEFT JOIN users 
          ON table1.user_id = users.id;

Also for your case make sure that there are no other insert or updates in between. otherwise use transactions.