Getting daily counts for events that don't happen every day - mysql

Question

I have a customer table in which a new row is inserted when a customer signup occurs.
Problem
I want to know the total number of signup per day for a given date range.
For example, find the total number of signup each day from 2015-07-01 to 2015-07-10
customer table
sample data [relevant columns shown]
customerid username created
1 mrbean 2015-06-01
2 tom 2015-07-01
3 jerry 2015-07-01
4 bond 2015-07-02
5 superman 2015-07-10
6 tintin 2015-08-01
7 batman 2015-08-01
8 joker 2015-08-01
Required Output
created signup
2015-07-01 2
2015-07-02 1
2015-07-03 0
2015-07-04 0
2015-07-05 0
2015-07-06 0
2015-07-07 0
2015-07-08 0
2015-07-09 0
2015-07-10 1
Query used
SELECT
DATE(created) AS created, COUNT(1) AS signup
FROM
customer
WHERE
DATE(created) BETWEEN '2015-07-01' AND '2015-07-10'
GROUP BY DATE(created)
ORDER BY DATE(created)
I am getting the following output:
created signup
2015-07-01 2
2015-07-02 1
2015-07-10 1
What modification should I make in the query to get the required output?

Answer 1

You're looking for a way to get all the days listed, even those days that aren't represented in your customer table. This is a notorious pain in the neck in SQL. That's because in its pure form SQL lacks the concept of a contiguous sequence of anything ... cardinal numbers, days, whatever.
So, you need to introduce a table containing a source of contiguous cardinal numbers, or dates, or something, and then LEFT JOIN your existing data to that table.
There are a few ways of doing that. One is to create yourself a calendar table with a row for every day in the present decade or century or whatever, then join to it. (That table won't be very big compared to the capability of a modern database.
Let's say you have that table, and it has a column named date. Then you'd do this.
SELECT calendar.date AS created,
ISNULL(a.customer_count, 0) AS customer_count
FROM calendar
LEFT JOIN (
SELECT COUNT(*) AS customer_count,
DATE(created) AS created
FROM customer
GROUP BY DATE(created)
) a ON calendar.date = a.created
WHERE calendar.date BETWEEN start AND finish
ORDER BY calendar.date
Notice a couple of things. First, the LEFT JOIN from the calendar table to your data set. If you use an ordinary JOIN the missing data in your data set will suppress the rows from the calendar.
Second, the ISNULL in the toplevel SELECT to turn the missing, null, values from your dataset into zero values.
Now, you ask, where can I get that calendar table? I respectfully suggest you look that up, and ask another question if you can't figure it out.
I wrote a little essay on this, which you can find here.http://www.plumislandmedia.net/mysql/filling-missing-data-sequences-cardinal-integers/

Answer 2

Look here
Create teble with calendar and join it in your query.

Answer 3

DECLARE #MinDate DATE = '2015-07-01',
#MaxDate DATE = '2015-07-10';
Create Table tblTempDates
(created date, signup int)
insert into tblTempDates
SELECT TOP (DATEDIFF(DAY, #MinDate, #MaxDate) + 1)
Date = DATEADD(DAY, ROW_NUMBER() OVER(ORDER BY a.object_id) - 1, #MinDate), 0 As Signup
FROM sys.all_objects a
CROSS JOIN sys.all_objects b;
Create Table tblTempQueryDates
(created date, signup int)
INSERT INTO tblTempQueryDates
SELECT
created AS created, COUNT(scandate) AS signup
FROM
customer
WHERE
created BETWEEN #MinDate AND #MaxDate
GROUP BY created
UPDATE tblTempDates
SET tblTempDates.signup = tblTempQueryDates.signup
FROM tblTempDates INNER JOIN
tblTempQueryDates ON tblTempDates.created = tblTempQueryDates.created
select * from tblTempDates
order by created
Drop Table tblTempDates
Drop Table tblTempQueryDates
Not pretty, but it gives you what you want.