One SQL interview question (row and column Interchange), SQL questions

One SQL interview question (row and column Interchange), SQL questions

There is a high probability that an SQL question will appear during the interview. Recently, some students will still encounter such a question during the interview. I would like to share with you here.

Question: The database has a table named sales as follows.

Year	Quarter	Sales Volume
1991	1	11
1991	2	12
1991	3	13
1991	4	14
1992	1	21
1992	2	22
1992	3	23
1992	4	24

Requirement: Write an SQL statement to query the result as follows.

Year	First Quarter	Quarter 2	Quarter 3	Fourth Quarter
1991	11	12	13	14
1992	21	22	23	24

The answer is as follows:

Select Year, sum (case when quarter = 1 then sales else 0 end) as First Quarter, sum (case when quarter = 2 then sales else 0 end) as second quarter, sum (case when quarter = 3 then sales else 0 end) as three quarter, sum (case when quarter = 4 then sales else 0 end) as four quarter from sales group by year;