Question

I cant seem to group by multiple data fields and sum a particular grouped column.

I want to group Person to customer and then group customer to price and then sum price. The person with the highest combined sum(price) should be listed in ascending order.

Example:

table customer
-----------
customer | common_id
 green        2
 blue         2
 orange       1

table invoice
 ----------
 person | price | common_id
 bob        2330     1
 greg       360      2    
 greg       170      2

SELECT DISTINCT
    min(person) As person,min(customer) AS customer, sum(price) as price
FROM invoice a LEFT JOIN customer b ON a.common_id = b.common_id 
GROUP BY customer,price
ORDER BY person

The results I desire are:

**BOB:** 
Orange, $2230

**GREG:**
green,  $360
blue,$170

The colors are the customer, that GREG and Bob handle. Each color has a price. 

Answer 1

There are two issues that I can see. One is a bit picky, and one is quite fundamental.

Presentation of data in SQL

SQL returns tabular data sets. It’s not able to return sub-sets with headings, looking something a Pivot Table.

The means that this is not possible…

**BOB:** 
Orange, $2230

**GREG:**
green,  $360
blue,   $170

But that this is possible…

Bob,  Orange, $2230
Greg, Green,  $360
Greg, Blue,   $170

Relating data

I can visually see how you relate the data together…

table customer                 table invoice
--------------                 -------------
customer | common_id           person | price |common_id
 green        2                 greg     360       2
 blue         2                 greg     170       2
 orange       1                 bob     2330       1

But SQL doesn’t have any implied ordering. Things can only be related if an expression can state that they are related. For example, the following is equally possible…

table customer                 table invoice
--------------                 -------------
customer | common_id           person | price |common_id
 green        2                 greg     170       2      \ These two have 
 blue         2                 greg     360       2      / been swapped
 orange       1                 bob     2330       1

This means that you need rules (and likely additional fields) that explicitly state which customer record matches which invoice record, especially when there are multiples in both with the same common_id.

An example of a rule could be, the lowest price always matches with the first customer alphabetically. But then, what happens if you have three records in customer for common_id = 2, but only two records in invoice for common_id = 2? Or do the number of records always match, and do you enforce that?

Most likely you need an extra piece (or pieces) of information to know which records relate to each other.