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Comment by chrislomax | Hacker News Reader

Without seeing any real data, wouldn't that all be a WHERE clause? I wouldn't imagine the skill was an aggregate of the applicants.

I've just skimmed over this though, I'm not having a go

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Ah I was trying to imply two sets of filtering and probably have them reversed, where HR is filtering on lack of honesty which only implies lack of skill or at least average skill, whereas the secondary filtration (the having clause) would imply the test for skill.

Don't you need a group by clause in order to have a having clause?

This is yet another of those things that gets the pgsql folks all wound up about mysql. mysql is generally permissive best effort rather than restrictive follow the spec, so HAVING is allowed to reference stuff not in a GROUP BY or an aggregate (like MAX or COUNT). As you imply, this is not allowed by the SQL standard so philosophically I would Strongly Expect pgsql to error out unlike mysql. I donno what ms-sql does, don't use microsoft stuff. Oracle costs too much, so another I donno.

About 99% of the noise about mysql vs pgsql boils down to this overarching philosophical different of "try yer best" vs "only perfection is permissible". There are minor other differences aside from that, none of which I can remember at this time.

I was mostly trying to make a joke and making the psuedocode kinda sql inspired rather than cut and paste into a window like a stack exchange answer. I could have implemented it "properly" as a nested subquery I suppose. Or to make the point a little more .. obviously, just "select 0;"

That's messed up. "Having" should only be used for filters on the output aggregate functions, and "where" should be used for filters on the input row data. If mysql lets you use "having" when you mean "where", that is unfortunate.

example:

    select count(1) cnt, department
    from sales
    where department_id in (1, 2, 3, 4, 5)
    group by department
    having count(1) >= 100;

So, it filters out all the input rows to only those department ids, and then it filters out the aggregate output rows to only those with a count() of 100 or more.

This is how Oracle and MS-SQL server work.

In SQL Server a HAVING without GROUP BY is a way to filter out duplicates.

It seems to error out.

  select name, count(*)
  from queries
  having count(*) > 1

Column 'queries.name' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Like this. There is more than one way to do it:

  -- List employees who have the biggest salary
  -- in their departments
  select
      Name
  from
      Employees e1
  where
      exists
      (
          select
              1
          from
              Employees e2
          where
              e2.DepartmentID = e1.DepartmentID
          having
              max(e2.Salary) = e1.Salary
      )

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