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This problem has two components: grouping totals by quarter, and creating crosstab output.
Grouping totals by quarter is easy if your database system has a date function that can extract the quarter from a date. For example, in Microsoft Access, you can write
select employeeno
, datepart("q",labordate) as quarter
, sum(laborhours) as sumhours
from yourtable
group
by employeeno
, datepart("q",labordate)
What if your database has no "quarter" date function? Then you could use the database's MONTH function. In order to group by quarter, we note that the quarters are given by months 1-3, 4-6, 7-9, and 10-12:
select employeeno
, case
when month(labordate) between 1 and 3
then 1
when month(labordate) between 4 and 6
then 2
when month(labordate) between 7 and 9
then 3
else 4
end as quarter
, sum(laborhours) as sumhours
from yourtable
group
by employeeno
, quarter
Instead of the CASE construct, you could also do arithmetic on the month number to come up with the quarter:
select employeeno
, cast( (month(labordate)+2) / 3
as integer )
as quarter
, ...
The only hitch with the two above approaches is that some databases may not let you use the column alias "quarter" in the GROUP BY clause, so you would have to repeat the CASE construct or the CAST function in the GROUP BY clause.
Finally, a solution using an integers table is:
select employeeno
, i as quarter
, sum(laborhours) as sumhours
from integers
inner
join yourtable
on i * 3 = month(labordate)
where i between 1 and 4
group
by employeeno
, i
The integers table is used in a similar way in Grouping output by week (24 October 2002).
But what about producing the output in a crosstab? Well, the best approach here is to use a reporting language. Microsoft Access has this built in, and it works really well.
However, if you do want to do it just with SQL, it would look like this:
select employeeno
, sum (
case
when month(labordate) between 1 and 3
then laborhours
else 0
end ) as quarter1hours
, sum (
case
when month(labordate) between 4 and 6
then laborhours
else 0
end ) as quarter2hours
, sum (
case
when month(labordate) between 7 and 9
then laborhours
else 0
end ) as quarter3hours
, sum (
case
when month(labordate) between 10 and 12
then laborhours
else 0
end ) as quarter4hours
from yourtable
group
by employeeno
This was first published in November 2002
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