MySQL: Find Missing Dates Between a Date Range

问题:

I need some help with a mysql query. I've got db table that has data from Jan 1, 2011 thru April 30, 2011. There should be a record for each date. I need to find out whether any date is missing from the table.

So for example, let's say that Feb 2, 2011 has no data. How do I find that date?

I've got the dates stored in a column called reportdatetime. The dates are stored in the format: 2011-05-10 0:00:00, which is May 5, 2011 12:00:00 am.

Any suggestions?

回答1:

This is a second answer, I'll post it separately.

SELECT DATE(r1.reportdate) + INTERVAL 1 DAY AS missing_date
FROM Reports r1
LEFT OUTER JOIN Reports r2 ON DATE(r1.reportdate) = DATE(r2.reportdate) - INTERVAL 1 DAY
WHERE r1.reportdate BETWEEN '2011-01-01' AND '2011-04-30' AND r2.reportdate IS NULL;

This is a self-join that reports a date such that no row exists with the date following.

This will find the first day in a gap, but if there are runs of multiple days missing it won't report all the dates in the gap.

回答2:

1. CREATE TABLE Days (day DATE PRIMARY KEY);

2. Fill Days with all the days you're looking for.

   mysql> INSERT INTO Days VALUES ('2011-01-01');
   mysql> SET @offset := 1;
   mysql> INSERT INTO Days SELECT day + INTERVAL @offset DAY FROM Days; SET @offset := @offset * 2;
   

   Then up-arrow and repeat the INSERT as many times as needed. It doubles the number of rows each time, so you can get four month's worth of rows in seven INSERTs.

3. Do an exclusion join to find the dates for which there is no match in your reports table:

   SELECT d.day FROM Days d 
   LEFT OUTER JOIN Reports r ON d.day = DATE(r.reportdatetime) 
   WHERE d.day BETWEEN '2011-01-01' AND '2011-04-30' 
       AND r.reportdatetime IS NULL;`
   

回答3:

It could be done with a more complicated single query, but I'll show a pseudo code with temp table just for illustration:

Get all dates for which we have records:

CREATE TEMP TABLE AllUsedDates

SELECT DISTINCT reportdatetime
INTO AllUsedDates;

now add May 1st so we track 04-30

INSERT INTO AllUsedData ('2011-05-01')

If there's no "next day", we found a gap:

SELECT A.NEXT_DAY
FROM
    (SELECT reportdatetime AS TODAY, DATEADD(reportdatetime, 1) AS NEXT_DAY FROM AllUsed Dates) AS A
WHERE
    (A.NEXT_DATE NOT IN (SELECT reportdatetime FROM AllUsedDates)
    AND
    A.TODAY <> '2011-05-01') --exclude the last day

回答4:

If you mean reportdatetime has the entry of "Feb 2, 2011" but other fields associated to that date are not present like below table snap

reportdate  col1    col2
5/10/2011   abc xyz
2/2/2011        
1/1/2011    bnv oda

then this query works fine

select reportdate from dtdiff where reportdate not in (select df1.reportdate from dtdiff df1, dtdiff df2 where df1.col1 = df2.col1)