Q
Problem solve Get help with specific problems with your technologies, process and projects.

# Totals for one customer compared with totals for all

I am trying to retrieve records where I can compare two sums. For example, if customer 123 purchased a quantity...

of 10 Widget Model A's over a one month period, I want the same row to show how many Widget Model A's we sold to all customers. A widget is defined by five unique fields. And, even if we sold other Widget Models, I don't want to pull any other Widget Models if company 123 did not purchase them that month. All of the fields are retrieved from one table.

Since a widget is defined by five unique fields, we have to code the values for these, as well as for the customer and the time period. Allow me to invent the names of the five fields:

```select sum(quantity) as cust_qty
, ( select sum(quantity)
from orders
where product_class  = 'General'
and product_line   = 'Widgets'
and product_type   = 'Model A'
and product_status = 'active'
and product_flag   = 0
and purchdate >= '2005-02-01'
and purchdate <  '2005-03-01'
) as all_qty
from orders
where custid = 123
and product_class  = 'General'
and product_line   = 'Widgets'
and product_type   = 'Model A'
and product_status = 'active'
and product_flag   = 0
and purchdate >= '2005-02-01'
and purchdate <  '2005-03-01'```

Notice the subquery in the SELECT list. This is called a scalar subquery, because it produces a single (scalar) value, and thus can be used instead of a single column value on each row. The database optimizer will execute a scalar subquery like this, which is non-correlated, i.e. not tied to a particular row in the main query, only once, ahead of the main query, so that its result, the sum for all customers, can be inserted into each row selected by the main query.

The subquery could also have been written as a correlated subquery, to make it a little easier to write the query for any product:

```select sum(quantity) as cust_qty
, ( select sum(quantity)
from orders
where product_class  = O.product_class
and product_line   = O.product_line
and product_type   = O.product_type
and product_status = O.product_status
and product_flag   = O.product_flag
and purchdate >= '2005-02-01'
and purchdate <  '2005-03-01'
) as all_qty
from orders as O

where custid = 123
and product_class  = 'General'
and product_line   = 'Widgets'
and product_type   = 'Model A'
and product_status = 'active'
and product_flag   = 0
and purchdate >= '2005-02-01'
and purchdate <  '2005-03-01'```

But now the optimizer might execute the scalar subquery once for each row that satisfies the criteria of the WHERE clause. This might not be as efficient, unless the optimizer realizes that there is an implicit GROUP BY and that there is actually only one group. So you may actually want to code the five widget field values twice.

Note also that it would not be quite so easy to correlate the time period, so it's usually more efficient just to code the time period end-points twice too.

This was last published in March 2005

#### Have a question for an expert?

Get answers from a TechTarget expert on whatever's puzzling you.

You will be able to add details on the next page.

#### Start the conversation

Send me notifications when other members comment.

## SearchDataManagement

• ### Focus, scope and spotting opportunity are key to role of CDO

Chief data officers and experts see the CDO role as changing to a more strategic orientation -- especially finding key ...

• ### Good data quality for machine learning is an analytics must

As companies add machine learning applications, they need to really understand -- and be able to improve -- their data. That's ...

• ### Chief data officer role: Searching for consensus

The chief data officer role is about many things -- regulations, innovation, AI and more. Consultant Randy Bean discussed the ...

• ### Data analytics in government efforts lack structure

Data analytics in government agencies lack organization, focusing on immediate problems instead of attacking underlying causes ...

• ### A complete guide to buying data discovery software

Data discovery software turns data into business insights, and it's vital for GDPR compliance. This guide outlines the products ...

• ### Rising demand for business analytics education programs

Colleges and universities are increasingly offering business analytics degrees. The graduates can help build IT and business ...

## SearchSAP

• ### On-premises, hosted most popular S/4HANA deployment options

The pure cloud -- SaaS -- version of SAP's newest ERP, S/4HANA Cloud, lacks some of the same features of the on-premises version....

• ### S/4HANA public cloud version can get lost in cloud confusion

The 'true' public cloud is the streamlined SaaS version of on-premises S/4. But private cloud options are often conflated with ...

• ### SAP S/4HANA migration: What you need to know

There's a lot to consider when contemplating a move to SAP S/4HANA, and this essential guide provides a starting point, including...

## SearchSQLServer

• ### Six sample databases for SQL Server and how to find them

SQL Server sample databases are useful for test and dev, but they can be difficult to parse. Use this SQL database sample ...

• ### A quick tutorial on SQL Server maintenance plans

SQL Server maintenance plans get a bad rap, but for DBAs who need a simple way to maintain databases, Microsoft's built-in tools ...

• ### Proposed Microsoft-GitHub buy confirms open source role in cloud

The looming Microsoft-GitHub pairing confirms the company's rebirth as an open source friend. Data tools on the Azure cloud are ...

## TheServerSide.com

• ### Jenkins Git integration: GitHub pull request via the Git plugin

This Jenkins Git integration tutorial demonstrates how to create a freestyle build job that performs a Jenkins GitHub pull ...

• ### Financial firms, vendors push self-service software delivery

Self-service DevOps automation appeals to enterprises that must push out new code as they adapt to changing requirements.

• ### IT projects and software teams need to include Agile people

Not every idea deserves equal weight in a software development project, but Agile people know that garnering input from a wide ...

## SearchDataCenter

• ### Four top open source SIEM tools you should know

Open source SIEM software offers organizations a way to test capabilities and augment existing functionalities for analytics and ...

• ### Rackspace colocation program hosts users' legacy servers

Rackspace now has a managed colocation program that it hopes to upsell its customers with additional services, once their servers...

• ### Broadcom acquisition of CA seeks broader portfolio

Broadcom has acquired CA Technologies in a move some believe is largely financially motivated, while others see an opportunity ...

## SearchContentManagement

• ### At OpenText Enterprise World, security and AI take center stage

OpenText unveiled its new application, OT2, at OpenText Enterprise World 2018, while also touting the importance of security. ...

• ### Augmented reality devices speed van repairs at Volkswagen U.K.

Augmented reality headsets for garage mechanics speed collaboration between repair shops and experts in the home office to solve ...

• ### Endpoint security tool fueled OpenText's Guidance Software acquisition

Endpoint security was the primary draw for OpenText's Guidance Software acquisition. But plans to improve e-discovery and data ...

## SearchHRSoftware

• ### Mindfulness technology helps companies bolster worker well-being

In discussing how to bring mindfulness programs into enterprises, vendors explain details on what works for employees, how ...

• ### Cost, doubt about tech hold back AI for HR investment

AI technology will improve the productivity of HR departments by eliminating many routine and transactional processes. But what ...

• ### Health and wellness benefits are exploding; are you keeping up?

A WorldatWork survey shows companies offered a wide variety of health and wellness benefits at an expanded rate last year. Is ...

Close