Question

How would I get a query that joins these four tables, and also gives me the average?

Table1:
TeamId |   TeamName
  1    |      TA
  2    |      TB
  3    |      TC

Table2:
YearsId  | Years
    1    | 2009-2010
    2    | 2010-2011
    3    | 2011-2012

Table3:
MonthsId | Month
    1    |  July
    2    |  Aug
    3    |  Sept

Table4:
TeamId  | MonthsId  | YearsId  | TeamWinCount
    1   |     1     |    2     |        44
    1   |     1     |    3     |        11
    1   |     2     |    2     |        0
    1   |     12    |    3     |        13
    2   |     1     |    2     |        33

I would like to get results that look like this:

   Year    |  Team   | Avg (avg win count jun+aug+sept+.../12)
 2009-2010 |   TA    |   23.3
 2009-2010 |   TB    |   18.23    
 2009-2010 |   TC    |   35.23    
 2010-2011 |   TA    |   18.23    
 2010-2011 |   TB    |   18.23    
 2010-2011 |   TC    |   18.23    

If there is no entry for a month, it should be counted as 0

There must be some genius out there’s that’s done this before. I’ve played around with joining the tables, but can’t seem to get a column that is the average. Any help or direction is much appreciated!

Answer 1

Table3 is not needed here

SELECT Table2.Years,Table1.TeamName,IFNULL(AVG(TeamWinCount), 0) AS TeamWinCount
FROM Table2
CROSS JOIN Table1
LEFT JOIN Table4 ON Table1.TeamId=Table4.TeamId AND Table2.YearsId=Table4.YearsId
GROUP BY Table2.Years,Table1.TeamName