SQL Workshop - Selecting columns without a non-aggregate column
Written by Nikos Vaggalis   
Thursday, 19 December 2013
Article Index
SQL Workshop - Selecting columns without a non-aggregate column
The Solution

That’s happening because column m.unit is used in the SELECT clause but not in the GROUP BY clause.

This is a perfectly valid and reasonable response from our DBMS, but in this exceptional case, selecting columns without including a non-aggregate column in the group by clause would be handy.

But this can’t happen if we are not explicit in what we ask for :

SELECT
 a.account_category,
 a.account_id,
 sum (b.value) as summed_amount 
FROM (
 SELECT m.material_id, m.year
 CASE 

  WHEN m.unit = 'PIECES'
   THEN m.mean_value * r.quantity * m.ratio 

   ELSE m.mean_value * r.quantity / m.ratio
  END as value
 from materials m, requests r
 where r.year = '1/1/13' and
       r.year = m.year and
       r.material_id = m.material_id) b,
                              accounts a
WHERE
    a.material_id = b.material_id and
    a.year = b.year
GROUP BY account_category, account_id

This works because of an inline view (marked in red) which acts as a temporary table holding the value for each row :

 

Result Set 3

Material_id

Year

Value

TX002

1/1/2013

$360

TX003

1/1/2013

$680.01

 

and exporting material_id and year to the outside scope, both of which will subsequently used for joining with the Accounts table of the outer query ( a.material_id = b.material_id and a.year = b.year), producing :

 

Result Set 4

Account_category

Account_id

Value

01

220201511

$360

01

220201511

$680.01

 

and finally grouped into :

 

Result Set 5

Account_category

Account_id

Summed_amount

01

220201511

$1040.01


enabling us to answer questions like “how much money on average, did the consumption of fruit cost us this year?”, so that we can estimate how much money we should reserve for next year’s purchases.

Other SQL Workshops

SQL Workshop - Selecting columns without including a
non-aggregate column in the group by clause

SQL Workshop - Subselects And Join

 

More SQL Workshop soon!

Related Articles

SQL Server: Quickly get row counts for tables, heaps, indexes, and partitions

The First Things I Look At On A SQL Server – Part 1

The First Things I Look At On A SQL Server – Part 2

A Generic SQL Server Compression Utility

Codd and his Rules      

 

To be informed about new articles on I Programmer, install the I Programmer Toolbar, subscribe to the RSS feed, follow us on, Twitter, FacebookGoogle+ or Linkedin,  or sign up for our weekly newsletter.

 SQLW

 

espbook

 

Comments




or email your comment to: comments@i-programmer.info

 

Banner


pg_parquet - Postgres To Parquet Interoperability
28/11/2024

pg_parquet is a new extension by Crunchy Data that allows a PostgreSQL instance to work with Parquet files. With pg_duckdb, pg_analytics and pg_mooncake all of which can access Parquet files, is  [ ... ]



Advent Of Code 2024 Now Underway
01/12/2024

December 1st is much anticipated among those who like programming puzzles. It is time to start solving small but tricky puzzles on the Advent of Code website with the goal of amassing 50 stars by Chri [ ... ]


More News

 



Last Updated ( Thursday, 06 September 2018 )