Question

I have thus two tables:

 CREATE TABLE `workers` (
  `id` int(7) NOT NULL AUTO_INCREMENT,
  `number` int(7) NOT NULL,
  `percent` int(3) NOT NULL,
  `order` int(7) NOT NULL,
      PRIMARY KEY (`id`)
 );
 CREATE `data` (
  `id` bigint(15) NOT NULL AUTO_INCREMENT,
  `workerId` int(7) NOT NULL,
  PRIMARY KEY (`id`)
 );

I want to return the first worker (order by order ASC) that his number of rows in the table data times percent(from table workers) /100 is smaller than number(from table workers.

I have tried this query:

SELECT workers.id, COUNT(data.id) AS `countOfData`
FROM `workers` as workers, `data` as data
WHERE data.workerId = workers.id
   AND workers.percent * `countOfData` < workers.number
LIMIT 1

But I get the error:

#1054 - Unknown column 'countOfData' in 'where clause'

Answer 1

This should work:

SELECT A.id
FROM workers A
LEFT JOIN (SELECT workerId, COUNT(*) AS Quant
            FROM data
            GROUP BY workerId) B
ON A.id = B.workerId
WHERE (COALESCE(Quant,0) * `percent`)/100 < `number`
ORDER BY `order`
LIMIT 1