flysolomin / flysolomin-groupby

Background

SQL sublanguage: DQL (Data Query Language)

NOTE: Before attempting this activity, you should have already completed the Order By and Aggregate Functions activities.

The GROUP BY clause allows you to group your results and can be used with the ORDER BY clause. GROUP BY is used in conjunction with aggregate functions. However, you cannot group by the output of the function. Recall that the output of an aggregate function is a single aggregate value.

employee table

id	employee	manager	salary
1	'Steve'	'Dave'	67400.00
2	'Alexa'	'Dave'	42500.00
3	'Sarah'	'Jane'	99890.99
4	'Brandon'	'Jane'	120000
5	'Adam'	'Dave'	55050.50

Example: You could query the above table with the AVG() aggregate function and GROUP BY manager to find the average salary of employees under that manager (then order it from greatest average salary to least):

SELECT manager, AVG(salary)
FROM employees
GROUP BY manager
ORDER BY AVG(salary) DESC;

Additional Reference if needed: https://www.w3schools.com/sql/sql_groupby.asp

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Lab

Problem 1

song table

id	artist	album	song
1	'The Beatles'	'Abbey Road'	'Come Together'
2	'The Beatles'	'Let It Be'	'Let It Be'
3	'Led Zeppelin'	'IV'	'Black Dog'
4	'Led Zeppelin'	'Physical Graffiti'	'Kashmir'
5	'Led Zeppelin'	'IV'	'Going to California'
6	'The Eagles'	'Hotel California'	'Hotel California'

Problem 1: Use the GROUP BY clause with the COUNT() aggregate function to query the song table for the number of songs by each artist. The result of the query should have two columns: the artist, and the count(song) of the artist.

HINT: You should avoid using the wild card (*) in your statement. All projected columns must either be used in the GROUP BY clause or an aggregate function.