"I've isolated the bug to a database query"

Re:"I've isolated the bug to a database query" by endersshadow on Wednesday November 09, 2011 @12:14PM (#3216345)

I don't think I've ever used a right join in a production query (perhaps a couple of times when I was doing some digging and it was easier), but I don't understand your statement. Left joins are insanely useful. For example, getting all the sales for a salesperson:

    select
        sp.Name,
        sum(s.Amount) as TotalSales
    from
        SalesPerson sp
        left join Sales s on
            sp.SalesPersonKey = s.SalesPersonKey
    group by
        sp.Name
    order by
        TotalSales desc

If you did a correlated subquery, it would take a ton of time to complete (`select sum(Amount) from Sales s where s.SalesPersonKey = sp.SalesPersonKey`), especially on large tables.

Left joins (and full outer joins) are plenty useful and I use them almost daily. Care to explain what you mean?

[ Parent | on HN ]

Re:"I've isolated the bug to a database query" by ckuehne on Wednesday November 09, 2011 @12:27PM (#3216409)

What he (probably) means is that the following query returns the same result as your query:

    select
        sp.Name,
        sum(s.Amount) as TotalSales
    from
        Sales s
        RIGHT join SalesPerson sp on
            sp.SalesPersonKey = s.SalesPersonKey
    group by
        sp.Name
    order by
        TotalSales desc

EDIT: Formatting.

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Re:"I've isolated the bug to a database query" by jtheory on Thursday November 10, 2011 @07:50AM (#3219862)

That's what was meant, I assume, but it's misguided. Right joins don't create a "code smell" for technical reasons, but for practical reasons. Because left joins are the standard approach, if you're using a non-standard approach to a common problem you'd better have a damned good reason (because you're just confusing maintenance programmers... and thus causing errors... with no justification, otherwise).

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