Question

I am currently doing the following join and it takes a very long time to execute the query, is there a way to make it run quicker?
I have 23 fields in the table. I have a primary key on the field ‘id’ (int) 5
reg (varchar) 9

SELECT a1.*, ( SELECT COUNT(reg) FROM auction a2 WHERE reg = a1.reg) AS c1 FROM auction a1


CREATE TABLE IF NOT EXISTS `db1` (
  `id` int(5) unsigned NOT NULL AUTO_INCREMENT,
  `adate` varchar(10) NOT NULL,
  `lnu` int(4) NOT NULL,
  `reg` varchar(9) NOT NULL,
  `mk` varchar(50) NOT NULL,
  `mod` varchar(50) NOT NULL,
  `type` varchar(25) NOT NULL,
  `ree` varchar(50) NOT NULL,
  `co` varchar(50) NOT NULL,
  `fu` varchar(20) NOT NULL,
  `tran` varchar(20) NOT NULL,
  `mt` varchar(9) NOT NULL,
  `mile` int(6) NOT NULL,
  `ree` int(6) NOT NULL,
  `apv` int(6) NOT NULL,
  `ds` int(2) NOT NULL,
  `sr` varchar(50) NOT NULL,
  `sen` int(10) NOT NULL,
  `keep` int(2) unsigned NOT NULL,
  `tmp` char(1) DEFAULT NULL,
  `rk` varchar(100) DEFAULT NULL,
  `st` varchar(3) DEFAULT NULL,
  `dd` varchar(10) DEFAULT NULL,
  PRIMARY KEY (`id`),
  KEY `date` (`adate`)

Answer 1

Seeing fromyour current schema, you should have provided index on reg column.

SELECT a1.*, a2.totalCount
FROM    auction a1
        INNER JOIN 
        (
            SELECT reg, COUNT(*)  totalCount
            FROM auction a2
            GROUP BY reg
        ) a2 
            ON a2.reg = a1.reg