Return 0 as default value for values in BETWEEN range-CodePudding

I have a query which is supposed to fetch data added to a table in the last 14 days. Now the issue is that the table might not have data for a particular date or might not have data at all. But I want to have a scenario where the result could have all dates from the last 14 dates and return the result count if available or return 0 as default.

My query currently:

SELECT b.created_at day, COUNT(b.id) count
FROM businesses b
WHERE b.created_at BETWEEN SUBDATE(NOW(), 14) AND NOW()
GROUP BY b.created_at

Sample table:

id    created_at
1     2021-11-20
2     2021-11-20
3     2021-11-19
4     2021-11-18
5     2021-11-17

The above query ran on the above table will produce something like this:

day           count
2021-11-20    2 
2021-11-19    1
2021-11-18    1
2021-11-17    1

What i wish to achieve should look like this; using the current date as 2021-11-22

day           count
2021-11-22    0 
2021-11-21    0
2021-11-20    2
2021-11-19    1
2021-11-18    1
2021-11-17    1
2021-11-16    0
2021-11-15    0
2021-11-14    0
2021-11-13    0
2021-11-12    0
2021-11-11    0
2021-11-10    0
2021-11-09    0

From the above query, the WHERE clause checks for created_at values between the current date and a 14 days interval backwards. The table obviously won't have data for all of the dates which is why i wish to return 0 for such dates. How to go about this please. Thanks.

CodePudding user response：

I suppose created_at is DATE not DATETIME, otherwise DATE(created_at) should be used.

add a helper table with running number 0 - 13 to generate rows with missing data.

SELECT DATE(NOW()) - INTERVAL n.diff DAY AS day, COALESCE(d.counts, 0)
FROM (
  SELECT 0 diff UNION SELECT 1 UNION SELECT 2 UNION SELECT 3 UNION SELECT 4 UNION SELECT 5 UNION SELECT 6 
             UNION SELECT 7 UNION SELECT 8 UNION SELECT 9 UNION SELECT 10 UNION SELECT 11 UNION SELECT 12 UNION SELECT 13
) n
LEFT JOIN (
  SELECT b.created_at, COUNT(b.id) counts
  FROM businesses b
  WHERE b.created_at BETWEEN SUBDATE(NOW(), 14) AND NOW()
  GROUP BY b.created_at
) d ON d.created_at = DATE(NOW()) - INTERVAL n.diff DAY
ORDER BY day