Home > Articles > Data > SQL

This chapter is from the book

10.10 Grouping Sets

The GROUP BY clauses that have been described so far use the short notation for the specification of groupings. SQL also has a more extensive notation. So-called grouping sets specifications indicate on which expressions groupings must be performed.

Example 10.21. For each town, get the most recent date of birth.

With the shortest notation form, this statement looks as follows:

SELECT   TOWN, MIN(BIRTH_DATE)
FROM     PLAYERS
GROUP BY TOWN

When the extensive notation form is used, this similar formulation occurs:

SELECT   TOWN, MIN(BIRTH_DATE)
FROM     PLAYERS
GROUP BY GROUPING SETS ((TOWN))

The result of both statements is:

TOWN       MIN(BIRTH_DATE)
---------  ---------------
Stratford  1948-09-01
Midhurst   1963-06-22
Inglewood  1962-07-08
Plymouth   1963-10-01
Douglas    1963-05-14
Eltham     1964-12-28

Explanation: Behind the term GROUPING SETS, the grouping sets specifications can be found. Within such a specification, several groupings can be specified. Each grouping is placed between brackets and the whole should also be placed between brackets—hence, the double brackets.

The advantage of the extensive notation form is that it offers more ways to group data. Several groupings can be specified, among other things, and combinations of ROLLUP and CUBE can be used.

Example 10.22. For each town, get the number of players, and for each sex, get the number of players as well.

Because a grouping is needed on two different columns, this question cannot be formulated with one GROUP BY clause (in which the short notation form is used). A way to combine these two groupings in one statement is to use an UNION operator.

SELECT   CAST(NULL AS CHAR), TOWN, COUNT(*)
FROM     PLAYERS
GROUP BY TOWN
UNION
SELECT   SEX, CAST(NULL AS CHAR), COUNT(*)
FROM     PLAYERS
GROUP BY SEX
ORDER BY 2, 1

The result is:

SEX  TOWN       COUNT(*)
---  ---------  --------
?    Stratford         7
?    Midhurst          1
?    Inglewood         2
?    Plymouth          1
?    Douglas           1
?    Eltham            2
M    ?                 9
F    ?                 5

Explanation: The rows in this intermediate result in which the TOWN column has been filled came from the first select block. The rows in which TOWN is equal to NULL form the intermediate result of the second select block. In fact, these two rows form subtotals for each sex.

To simplify this type of statement, the grouping sets specification has been added to SQL. With this, one GROUP BY clause can be used to specify several groupings. The previous statement becomes:

SELECT   SEX, TOWN, COUNT(*)
FROM     PLAYERS
GROUP BY GROUPING SETS ((TOWN), (SEX))
ORDER BY 2, 1

Explanation: Behind the words GROUPING SETS, two groupings are now specified: (TOWN) and (SEX).

If one grouping consists of one expression, the brackets can be removed. So, GROUP BY GROUPING SETS ((TOWN), (SEX)) is equivalent to GROUP BY GROUPING SETS (TOWN, SEX).

Again, the GROUP BY clause, as we discussed in the previous chapters, is, in fact, a shortened notation for the one with grouping sets. Table 10.1 contains several examples of original formulations without grouping sets and their equivalents with grouping sets.

Table 10.1. Original GROUP BY Clauses and Their Equivalent Grouping Sets Specifications

Original Specification

Specification with Grouping Sets

GROUP BY A

GROUP BY GROUPING SETS ((A))

or

GROUP BY GROUPING SETS (A)

GROUP BY A, B

GROUP BY GROUPING SETS ((A, B))

GROUP BY YEAR(A), SUBSTR(B)

GROUP BY GROUPING SETS ((YEAR(A), SUBSTR(B)))

A special grouping is (). There is no expression between the brackets. In this case, all rows are placed in one group. We can calculate a grand total with that, for example.

Example 10.23. Find for each combination of sex-town the number of players, get for each sex the number of players, and get the total number of players in the entire table.

SELECT   SEX, TOWN, COUNT(*)
FROM     PLAYERS
GROUP BY GROUPING SETS ((SEX, TOWN), (SEX), ())
ORDER BY 1, 2

The result is:

SEX  TOWN       COUNT(*)
---  ---------  --------
M    Stratford         7
M    Inglewood         1
M    Douglas           1
M    ?                 9
F    Midhurst          1
F    Inglewood         1
F    Plymouth          1
F    Eltham            2
F    ?                 5
?    ?                14

Explanation: The last row contains the total number of players and is added because of the grouping ().

Example 10.24. Get for each team and for each player individually the number of matches played.

SELECT   TEAMNO, PLAYERNO, COUNT(*)
FROM     MATCHES
GROUP BY GROUPING SETS (TEAMNO, PLAYERNO)
ORDER BY 1, 2

The result is:

TEAMNO  PLAYERNO  COUNT(*)
------  --------  --------
     1         ?         8
     2         ?         5
     ?         2         1
     ?         6         3
     ?         8         2
     ?        27         1
     ?        44         1
     ?        57         1
     ?        83         1
     ?       104         1
     ?       112         2

Explanation: The first two rows in the result have been included because of the grouping on the TEAMNO column and the other rows because of the grouping on the PLAYERNO column.

This example clearly shows that brackets are important. The specification GROUPING SETS (TEAMNO, PLAYERNO) returns a different result than GROUPING SETS ((TEAMNO, PLAYERNO)). The second grouping sets specification results in one grouping on the combination of the two columns specified and the second grouping sets specification leads to two groupings.

Finally, here are a few abstract examples of certain GROUP BY clauses, including the groupings that are executed. E1, E2, and E3 stand for random expressions, and the symbol ∪ represents the union operator.

Table 10.2. The Relationship Between Grouping Sets Specifications and Groupings

GROUP BY Clause

Groupings

GROUP BY E1, E2, E3

[E1, E2, E3]

GROUP BY GROUPING SETS (())

[]

GROUP BY GROUPING SETS ((E1, E2, E3))

[E1, E2, E3]

GROUP BY GROUPING SETS (E1, E2, E3)

[E1] ∪ [E2] ∪ [E3]

GROUP BY GROUPING SETS ((E1), (E2), (E3))

[E1] ∪ [E2] ∪ [E3]

GROUP BY GROUPING SETS ((E1, E2), (E3))

[E1, E2] ∪ [E3]

GROUP BY GROUPING SETS ((E1, E2), E3)

[E1, E2] ∪ [E3]

GROUP BY GROUPING SETS ((E1, E2), (E3, E4))

[E1, E2] ∪ [E3, E4]

GROUP BY GROUPING SETS ((E1, (E2, E3)))

Not allowed

Exercise 10.24: Get the total number of penalties by using a grouping sets specification.

Exercise 10.25: Get for each combination of team number and player number the number of matches, give the number of matches for each team number, and find the total number of matches as well.

Exercise 10.26: Indicate which groupings must be specified for the following GROUP BY clauses:

  1. GROUP BY GROUPING SETS ((), (), (E1), (E2))
  2. GROUP BY GROUPING SETS (E1, (E2, E3),(E3, E4, E5))
  3. GROUP BY GROUPING SETS ((E1, E2), (), E3, (E2, E1))

InformIT Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from InformIT and its family of brands. I can unsubscribe at any time.

Overview


Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information


To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites, develop new products and services, conduct educational research and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@informit.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information


Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security


Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children


This site is not directed to children under the age of 13.

Marketing


Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information


If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out


Users can always make an informed choice as to whether they should proceed with certain services offered by InformIT. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.informit.com/u.aspx.

Sale of Personal Information


Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents


California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure


Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links


This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact


Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice


We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020