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Combining UNION and LIMIT operations in MySQL query

Posted by: admin November 1, 2017 Leave a comment

Questions:

I have a Jobs and a Companies table, and I want to extract 20 jobs that meet the following criteria:

  1. Jobs only from two (2) named companies
  2. There can at most be 10 jobs per company

I have tried the following SELECT with UNION DISTINCT, but the problem is that the LIMIT 0,10 applies to the whole result set. I want it to apply to each of the companies.

If there aren’t 10 jobs per company, then the query should return all the jobs it finds.

SELECT c.name, j.title, j.`desc`, j.link 
  FROM jobs_job j
INNER JOIN companies_company c ON j.company_id = c.id
WHERE c.name IN ('Company1')
UNION DISTINCT
SELECT c.name, j.title, j.`desc`, j.link 
  FROM jobs_job j
INNER JOIN companies_company c ON j.company_id = c.id
WHERE c.name IN ('Company2')
ORDER by name, title
LIMIT 0,10

I am new to MySQL, so realise there may be a smarter way to do this instead of with UNION, so any suggestions for improvements are definitely welcome.

Answers:

Quoting the docs,

To apply ORDER BY or LIMIT to an
individual SELECT, place the clause
inside the parentheses that enclose
the SELECT:

(SELECT a FROM t1 WHERE a=10 AND B=1 ORDER BY a LIMIT 10)
UNION
(SELECT a FROM t2 WHERE a=11 AND B=2 ORDER BY a LIMIT 10);