Question

Consider the following data.   

STUDENT
StudentID	SName	Gender	Age	ClubID
3234	Alfred Smith	Male	20	BSK
2244	McJohnson Robert	Male	22
2389	Jessica Low	Female	20	JPA
4211	Roland Devingo	Male	24
4383	Jane Usa Khan	Female	21	BKY
4450	Elaine Fong	Female	20	JPA

CLUB
ClubID	CName	Founded	Budget
BKY	Bakery Club	2010	2546
PDC	Photomedia and Design	2005	1345
JPA	Japanese Anime	2009	3453
BSK	Basketball	2011	6744

What is the value returned by this SQL statement?

SELECT COUNT( CLUBID )
FROM STUDENT

Answer 1

Given "STUDENT" table :

STUDENTID	SNAME	Gender	Age	ClubID
3234	Alfred Smith	Male	20	BSK
2244	McJohnson Robert	Male	22
2389	Jessica Low	Female	20	JPA
4211	Roland Devingo	Male	24
4383	Jane Usa Khan	Female	21	BKY
4450	Elaine Fong	Female	20	JPA

Given SQL statement as :

SELECT COUNT( CLUBID ) FROM STUDENT

Answer : By executing above SQL statement ,the output is as below :

  COUNT( CLUBID ) - - - - - - - - - - - - - - - - - - 4

Explanation : In given SQL statement, the COUNT() function with column name is used. It counts and returns the numbers of rows in a particular column from the given table.

• In given SQL statement , it is given that COUNT(CLUBID) so the count function counts the number of rows in "CLUBID" column from "STUDENT" table which are not null that means in "CLUBID" column of "STUDENT" table it counts the number of rows which are filled with values. It do not count the rows which are null(the rows which are empty or no value).
• The "CLUBID" column in "STUDENT" table , there are 4 rows which are not null.
• Therefore the returned value by given SQL statement is 4.

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