Question

In sql I want to show statistics data, so I’d like to show sums from all weekdays, by showing 0 for the weekday that doesn’t exist. Same goes with month, hours, years….

The problem is that there is no table to join to to get the missing days.
Is there a clean method to do this?

Thank you

Edit :
The DB and data is irrelevent but I’m using Oracle DB and Mysql, simply put if i want to do

SELECT SUM(SALES) FROM SALES_TABLE WHERE SALES_DATE BETWEEN DATE1 AND DATE2 GROUP BY WEEKDAY

how to change this to get 0 for example on sundays, and not get SATURDAY :4, MONDAY:4

Answer 1

You could create a table with day names in it, and then do a left join on that table.

It’d help to have a look at the table structure you have, but if I was going to do it, I’d do something like the following:

create table stats (dayname varchar(3), "value" int);
create table daynames (dayname varchar(3));
insert into stats values ('Sun', 5), ('Mon', 4), ('Wed', 13), ('Sun', 3), ('Tue', 5), ('Sat', 5), ('Mon', 32);
insert into daynames values ('Sun'),('Mon'),('Tue'),('Wed'),('Thu'),('Fri'),('Sat');

select daynames.dayname, sum("value") from daynames left outer join stats on stats.dayname=daynames.dayname group by daynames.dayname;

| dayname | sum |
|---------+-----|
| Fri     |     |
| Mon     | 36  |
| Sat     | 5   |
| Sun     | 8   |
| Thu     |     |
| Tue     | 5   |
| Wed     | 13  |

You’ll have nulls for the sums on dates that aren’t represented in your data, but you can convert them to zeros, depending on your database server.