Databases
StackOverflow2013
Postsdbo
POWhy do aggregates in subqueries have to be aggregated again?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POWhy do aggregates in subqueries have to be aggregated again?
    primarykey
    data
    text
    <p>I hope I've put the query together correctly below. I've simplified from something much, much bigger. But my question should be clear enough from the example.</p> <p>In the innermost query, <code>nest1</code>, let's say the results come back with three entries for invoice 123. The invoice was created (1), then two cash deposits were made (2, 3), the second of which (3), paid off the invoice. From that result set, I'm aggregating the sum. I'm also getting the paid_off_date, which only one of the rows will have. </p> <p>I'm happy to be schooled on better ways to design this query, but what I don't understand is why I have to select the aggregates all the way out. Why, for example, when I select <code>SUM(cash_deposit) AS 'cash_deposit'</code> in <code>nest2</code>, do I also have to select <code>SUM(cash_deposit)</code> in the outermost query? Once it is aggregated in a subquery, why isn't the aggregate passed along? And why do I have to keep grouping by id at each level? </p> <pre><code>SELECT id, SUM(cash_deposit), MAX(paid_off_date), MAX(job_phase), MAX(cust_id) FROM ( SELECT id AS id, SUM(cash_deposit) AS 'cash_deposit', MAX(paid_off_date) AS 'paid_off_date', MAX(job_phase) AS 'job_phase' FROM ( SELECT id, cash_deposit, paid_off_date FROM invoice GROUP BY id ) nest1 JOIN job j ON nest1.id = j.id GROUP BY id ) nest2 JOIN customer c ON c.invoice = nest2.id GROUP BY id </code></pre> <p><strong>Clarification</strong></p> <p>Thanks for any posts with improved versions of the query. I'm working with an existing query that produces unexpected results when I start trying to turn the nesting into joins. I'm going to keep playing with it, but I'd also really appreciate if someone could answer the question about aggregates and why they have to be repeated when nesting. In C#, I can sum up three numbers in one function and then pass the resulting value back. I don't have to keep summing the results. I need some help understanding how SQL subqueries function differently in that respect.</p> <p><strong>Possible Answer</strong></p> <p>One of my coworkers pointed out that in this case, It's because of my <code>GROUP BY</code> clauses. Since <code>cash_deposit</code> and <code>job_phase</code>, for example, aren't in the <code>GROUP BY</code> clause, they have to be aggregated.</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. UStmoore82
    1. UStmoore82
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload