MySQL COUNT - returns a null result, not NULL

Question

I am trying to return a result set from MySql, which is grouped by YEAR and MONTH, and which has an account returned for every YEAR / MONTH ..

This is where I started:

SELECT YEAR(p.pEndDate) AS pYear, MONTHNAME(p.pEndDate) AS pMonth, count(*) AS pNum 
FROM projects p
WHERE p.status=3
GROUP BY YEAR(p.pEndDate), MONTH(p.pEndDate)

This SQL basically does 90% of what I need, except when there is a month where the counter is zero. For example, in July 2009 there were zero projects with status 3, so I get:

2008    November    1
2009    January     2
2009    February    2
2009    March   2
2009    April   1
2009    May 2
2009    June    3
2009    August  2
2009    September   1
2009    October 1
2009    November    2
2009    December    1
2010    January 4
2010    February    1
2010    March   1
2010    April   3
2010    May 3
2010    June    3
2010    July    3
2010    August  3
2010    September   3
2010    October 2
2010    November    2
2010    December    3
2011    January 2
2011    February    1

Please note that July simply does not exist.

So, I started to do some research using another table to get the result set to include July. So I created a new table "monthTable" and added two columns monthID int Primary Key, monthName VARCHAR (3).

, RIGHT JOIN .. , , , , .

!

Answer 1

[monthTable], RIGHT JOIN .. , , , , .

FROM projects p WHERE p.status=3

, -

FROM projects p
RIGHT JOIN monthTable m on <join p to m>
WHERE p.status=3`

, WHERE , p.status(null). JOIN,

FROM projects p
RIGHT JOIN monthTable m on <join p to m> AND p.status=3`

, , , esp monthName varchar (3)?

monthID int Primary Key, monthName VARCHAR(3).

()

DROP PROCEDURE IF EXISTS FillMonthsTable;

delimiter //
CREATE PROCEDURE FillMonthsTable()
    LANGUAGE SQL
    NOT DETERMINISTIC
    CONTAINS SQL
    SQL SECURITY DEFINER
    COMMENT ''
BEGIN
  drop table if exists monthsTable;
  create table monthsTable (theYear int, theMonth int, monthName varchar(20));

  SET @x := date('2000-01-01');
  REPEAT 
    insert into monthsTable (theyear, themonth, monthname) SELECT year(@x), month(@x), monthname(@x);
    SET @x := date_add(@x, interval 1 month);
    UNTIL @x > date('2030-01-01') END REPEAT;
END//
delimiter ;

CALL FillMonthsTable;

DROP PROCEDURE FillMonthsTable;

, (1- , 0s)

SELECT m.theYear, m.theMonth, IFNULL(t.pNum, 0) theCount
FROM monthsTable m
LEFT JOIN (
    SELECT YEAR(p.pEndDate) AS pYear, MONTH(p.pEndDate) AS pMonth, count(*) AS pNum 
    FROM projects p
    WHERE p.status=3
    GROUP BY YEAR(p.pEndDate), MONTH(p.pEndDate)
) t on t.pYear = m.theYear and t.pMonth = m.theMonth
ORDER BY m.theYear, m.theMonth

Answer 2

OMG Ponies, Numbers Tally, , , .

Create Table Numbers ( Value int not null Primary Key )
Insert Numbers(Value) Values( 1 )
Insert Numbers(Value) Values( 2 )
...
Insert Numbers(Value) Values( 12 )
...
Insert Numbers(Value) Values( 2000 )
Insert Numbers(Value) Values( 2001 )
...
Insert Numbers(Value) Values( 2011 )
Insert Numbers(Value) Values( 2012 )

, , . Numbers:

Select Years.Value As PYear
    , Month_Name( Date_Add('2000-01-01', Interval Months.Value - 1 MONTH) ) As PMonth
    , Count( P.NonNullableCol ) As PNum
From Numbers As Months
    Cross Join Numbers As Years
    Left Join Projects As P
        On Year( P.PEnddate ) = Years.Value
            And Month( P.PEndDate ) = Months.Value
Where Months.Value Between 1 And 12
    And Years.Value Between 2008 And 2011
Group By Years.Value, Months.Value

---

. , , , , . Numbers, , .

Create Table Calendar ( DateValue date not null Primary Key )
Insert Calendar( DateValue ) Values( '2000-01-01' )
Insert Calendar( DateValue ) Values( '2000-01-02' )
Insert Calendar( DateValue ) Values( '2000-01-03' )
...
Insert Calendar( DateValue ) Values( '2011-03-01' )

Select Year( C.DateValue ) As PYear
    , Month( C.DateValue ) As PMonth
    , Count( P.NonNullableCol ) As PNum
From Calendar As C
    Left Join Projects As P
        On P.PEndDate = C.DateValue
Where C.DateValue Between '2008-11-01' And '2011-02-28'
Group By Year( C.DateValue ), Month( C.DateValue )

Answer 3

nums 0 9, . , count null , , . , 2004 2006 , , nums :

SELECT DISTINCT ADDDATE('2004-01-01',INTERVAL i.i+j.i+k.i MONTH) AS mydate
FROM nums i JOIN nums j  JOIN nums k ORDER BY mydate LIMIT 27;

, , ON ( = = ​​).

Here a similar query is executed on my own table (msds) to illustrate:

select year(mydate) theyear, monthname(mydate) themonth, coalesce(c,0) thecount
from

(select DISTINCT adddate('2004-01-01',INTERVAL i.i+j.i+k.i MONTH) as mydate
FROM ints i  JOIN ints j  join ints k ORDER BY mydate LIMIT 27) datelist

left join

(SELECT year(issue_date) as y, month(issue_date) as m, count(*) c FROM msds m where issue_date between '2004-01-01' and '2006-03-01'
group by y, m) mydata

on (year(mydate)=y and month(mydate)=m)