Question

I have 1 table with similar data:

CustomerID | ProjectID | DateListed | DateCompleted
123456     | 045       | 07-29-2010 | 04-03-2011
123456     | 123       | 10-12-2011 | 11-30-2011
123456     | 157       | 12-12-2011 | 02-10-2012
123456     | 258       | 06-07-2011 | NULL

Basically, a customer contacts us, we get a project on our list, and we mark it completed when we’re done with it.

What I’m after is a simple (you’d think, at least) count of all projects, with expected output like below:

YEAR | TotalListed | TotalCompleted
2010 |       1     |        0
2011 |       3     |        2
2012 |       0     |        1

However, my query below – because of the join – isn’t showing 2012’s count, because there’s been no listed project for 2012. However, I can’t really reverse the query, as then 2010’s count wouldn’t show up (since nothing was completed in 2010).

I’m open to any suggestions, or tips like how to do this. I’ve pondered a temp table, is that the best way to go? I’m open to anything that gets me what I need!

(If the code looks familiar, ya’ll helped me get the subquery made! MySQL Subquery with main query data variable)

SELECT YEAR(p1.DateListed) AS YearListed, COUNT(p1.ProjectID) As Listed, PreQuery.Completed  
FROM(
    SELECT YEAR(DateCompleted) AS YearCompleted, COUNT(ProjectID) AS Completed 
    FROM projects 
    WHERE CustomerID = 123456 AND DateListed >= DATE_SUB(Now(), INTERVAL 5 YEAR) 
    GROUP BY YEAR(DateCompleted)
) PreQuery 
RIGHT OUTER JOIN projects p1 ON PreQuery.YearCompleted = YEAR(p1.DateListed)
WHERE CustomerID = 123456 AND DateListed >= DATE_SUB(Now(), INTERVAL 5 YEAR)
GROUP BY YearListed 
ORDER BY p1.DateListed

Answer 1

After reviewing your table, query, and expected results – I believe I have found a more-revised query to suit your needs. It is a fairly-full rewrite of your existing query though, but I’ve tested it with your given data and received the same results you want/expect:

SELECT
    years.`year`,
    SUM(IF(YEAR(DateListed) = years.`year`, 1, 0)) AS TotalListed,
    SUM(IF(YEAR(DateCompleted) = years.`year`, 1, 0)) AS TotalCompleted
FROM
    projects
    LEFT JOIN (
        SELECT DISTINCT `year` FROM (
            SELECT YEAR(DateListed) AS `year` FROM projects
            UNION SELECT YEAR(DateCompleted) AS `year` FROM projects WHERE DateCompleted IS NOT NULL
        ) as year_inner
    ) AS years
        ON YEAR(DateListed) = `year`
        OR YEAR(DateCompleted) = `year`
WHERE
    CustomerID = 123456 AND DateListed >= DATE_SUB(Now(), INTERVAL 5 YEAR)
GROUP BY
    years.`year`
ORDER BY
    years.`year`

To explain, we should start with the inner query (aliased as year_inner). It selects a full list of years in the DateListed and DateCompleted columns and then selects a DISTINCT list of those to create the years alias sub-query. This sub-query is used to get a full list of “years” that we want data for. Doing it this way, opposed to a sub-query with counts and groupings will allow you to only have to define the WHERE clause on the outermost query (though, if efficiency becomes an issue with thousands and thousands of records, you could always add a WHERE clause to the inner query too; or an index to the date columns).

After we’ve built our inner queries, we join the projects table on the results with a LEFT JOIN for the DateListed or DateCompleted‘s YEAR() value – which will allow us to bring back null columns too!

For the field selections, we use the year column from our inner query to assure that we get a full list of years to display. Then, we compare the current row’s DateListed & DateCompleted YEAR() value to the current year; if they’re equal, add 1 – else add 0. When we GROUP BY year, our SUM() will count all of the 1’s for that year for each column and give you the output you want (hopefully, of course =P).