SQL queries ordering and grouping. RHS SOC 2 SQL query - ordering In a query producing a large result, it may be beneficial to order the result SQL.

SQL queriesordering and grouping

RHS – SOC 2

SQL query - ordering

• In a query producing a large result, it may be beneficial to order the result

• SQL allows us to order the result by any of the fields in the result

• We use the keyword ORDER BY

RHS – SOC 3


SELECT <fieldlist>FROM <tablename>WHERE <condition>ORDER BY <fieldname>

Which fields do I want

From what table do I want the fields

What conditions must the fields fulfill

What order are the results sorted in

RHS – SOC 4


• We use a movie information database as example

Movie movieid title country prodyear genre oscars

Actor actorid name country birth living oscars

Casting movieid actorid

RHS – SOC 5

SQL query - orderingmovieid title country prodyear genre oscars

1 E.T. USA 1982 Sci-Fi 4

2 Taxi France 1998 Comedy 0

3 Hunger Denmark 1966 Drama 1

4 Leon France 1994 Thriller 0

5 Hard Boiled HK 1992 Action 0

6 1984 UK 1984 Sci-Fi 2

7 Seven USA 1995 Thriller 1

SELECT *FROM MovieORDER BY title

RHS – SOC 6


6 1984 UK 1984 Sci-Fi 2







SELECT *FROM MovieORDER BY title

RHS – SOC 7







6 1984 UK 1984 Sci-Fi 2


SELECT title, prodyearFROM MovieWHERE oscars > 0ORDER BY title

RHS – SOC 8







6 1984 UK 1984 Sci-Fi 2


SELECT title, prodyearFROM MovieWHERE oscars > 0ORDER BY title

RHS – SOC 9

SQL query - orderingtitle prodyear

1984 1984

E.T. 1982

Hunger 1966

Seven 1995 SELECT title, prodyearFROM MovieWHERE oscars > 0ORDER BY title

RHS – SOC 10


• We can even specifiy more than one field for ordering – secondary fields used if primary fields are identical

• We can choose between descending and ascending order, using the keywords DESC and ASC, respectively

ORDER BY oscars DESC, prodyear ASC

RHS – SOC 11

SQL query - functions

• We can even do some (simple) arithmetic in SQL, using a basic set of functions– COUNT– SUM– AVG– MIN– MAX

• These are called aggregate functions

RHS – SOC 12


• A aggregate function works on the values of a specific field (column)

• The set of values is determined by the search conditions

SELECT COUNT(title)FROM MovieWHERE (oscars > 0)

How many movies have won an Oscar

RHS – SOC 13


• This query can also be written asSELECT COUNT(title) AS OscarWinnersFROM MovieWHERE (oscars > 0)

• The AS keyword allows us to rename a column in the search result

• Only cosmetic, but useful…

NB!

RHS – SOC 14


SELECT COUNT(title) AS OscarWinners,

AVG(oscars) AS averageOscars,

MAX(oscars) AS maximalOscars

FROM MovieWHERE (oscars > 0)

RHS – SOC 15


OscarWinners averageOscars maximalOscars

4 2.0000 4

RHS – SOC 16

Exercise 4 – SQL queries• Use the MovieInformation database, defined in exercise 1• With the data in place, run the below queries on the database

– SELECT * FROM Movie ORDER BY prodyear ASC– SELECT title, prodyear FROM Movie ORDER BY title– SELECT MAX(prodyear) AS maxUSA FROM Movie WHERE country = ’USA’– SELECT AVG(prodyear) AS loserYear FROM Movie WHERE (oscars = 0)

• Now formulate queries yourself, in order to retrieve the below data:– Get all oscar-winning movies ordered by year (oldest movie first)– Get a sorted list of movie title for movies made in France– Get the year for the oldest movie not winning any Oscars– Get the average number of Oscars for Sci-Fi movies– Get the total number of Oscars won by movies from USA

RHS – SOC 17

SQL query - grouping

• The aggregate functions are good for calculating properties for the entire result of the search

• We may sometimes wish to find proper-ties for a certain group within the result

• This can be done using WHERE…• …but can be cumbersome if the groups

are very numerous

RHS – SOC 18


• Suppose we have a full movie database, with movies for more than 100 countries

• ”Find the total number of movies made in each country”

SELECT COUNT(title) AS MovieCountFROM MoviesWHERE country = ’…’

• More than 100 queries…

RHS – SOC 19


• A much easier way is to use GROUP BY• Syntax:

SELECT <fieldlist>FROM <tablename>GROUP BY <fieldlist>

• Produces a result for each group, specified in the field list

RHS – SOC 20

SQL query - groupingmovieid title country prodyear genre oscars






6 1984 UK 1984 Sci-Fi 2


SELECT country,COUNT(title) AS MovieCount

FROM MovieGROUP BY country

RHS – SOC 21







6 1984 UK 1984 Sci-Fi 2


SELECT country,COUNT(title) AS MovieCount

FROM MovieGROUP BY country

RHS – SOC 22

SQL query - groupingCountry MovieCount

Denmark 1

France 2

HK 1

UK 1

USA 2

RHS – SOC 23

SQL query - groupingCountry OscarTotal

Denmark 1

France 0

HK 0

UK 2

USA 5

SUM(oscars) AS …

RHS – SOC 24


• In the last example, it might be desirable to leave out results where total is zero

• In general; only include groups which fulfill some criteria

• This can be done using the HAVING keyword

RHS – SOC 25


• Syntax:SELECT <fieldlist>FROM <tablename>GROUP BY <fieldlist>HAVING <criteria>

RHS – SOC 26







6 1984 UK 1984 Sci-Fi 2


SELECT country,SUM(oscars) AS OscarTotal

FROM MovieGROUP BY countryHAVING (SUM(oscars) > 0)

RHS – SOC 27







6 1984 UK 1984 Sci-Fi 2


SELECT country,SUM(oscars) AS OscarTotal

FROM MovieGROUP BY countryHAVING (SUM(oscars) > 0)

RHS – SOC 28

SQL query - groupingCountry OscarTotal

USA 5

France 0

UK 2

HK 0

Denmark 1

RHS – SOC 29


Country OscarTotal

USA 5

UK 2

Denmark 1

RHS – SOC 30


• But wait…• …isn’t HAVING the same as WHERE..?• Not quite

– WHERE is for filtering out specific records– HAVING is for filtering out specific groups

from the final result• We cannot use an aggregate function in a

WHERE clause

RHS – SOC 31

Exercise 5 – SQL queries• Use the MovieInformation database, defined in exercise 1• With the data in place, run the below queries on the database

– SELECT genre, AVG(oscars) FROM Movie GROUP BY genre– SELECT oscars, MAX(prodyear) FROM Movie WHERE (oscars > 0) GROUP BY

oscars– SELECT genre, AVG(oscars) FROM Movie GROUP BY genre HAVING

(COUNT(title) > 1)

• Now formulate queries yourself, in order to retrieve the below data:– Get a list of the total count of movies, grouped by country. Within each

contry group, the count should be grouped by genre– Get a list of the average number of oscars won by movies, grouped by

country– Get a list of the total count of movies, grouped by country. Only include

movies made after 1985

SQL queries ordering and grouping. RHS SOC 2 SQL query - ordering In a query producing a large result, it may be beneficial to order the result SQL.

Documents