如果联接列中的值为空，则联接两个表并仅在一个表上产生结果

Question

I have table Quota with columns 'Month Number', 'year','Goal' as below

I have other table Sales with columns 'id', 'Sale Date' as below.

I am joining both the tables on Month and year of 'sales date' from Sales table to 'Month Number' and 'year' from Quota Table to get the results and i am able to get results if i have sales for that particular month and year.Now for the month of may i have no sales so when i join on those columns i am not getting any results from quota table. how can i just display Quota table values if there are no corresponding sales in Sales table? I tried left joining but its not displaying any results.

Answer 1

Like already said, we don't know your desired output. But by using a left join you should retrieve the records from the quota table.

declare @quota table (monthnumber int, qyear int, goal int)
insert into @quota values
(2,2017,5),
(3,2017,10),
(4,2017,8),
(5,2017,8),
(6,2017,10)

declare @sales table (id int, salesdate date)
insert into @sales values
(101,'20170321'),
(102,'20170427'),
(103,'20170223'),
(105,'20170427'),
(108,'20170321'),
(109,null),
(111,null)

select q.*
from @quota as q
    left outer join @sales as s
        on year(s.salesdate) = q.qyear and 
           month(s.salesdate) = q.monthnumber

Returns

monthnumber qyear   goal
--------------------------
2           2017    5
3           2017    10
3           2017    10
4           2017    8
4           2017    8
5           2017    8
6           2017    10

Answer 2

You can use month and year of function and do left join as below

select * from Quota q left join sales s
on q.year = year(s.saledate) and q.MonthNumber = month(s.saledate)

Answer 3

Despite you didn't specify what output you need or your effort so far, I made my attempt anyway and I guess this is what you want:

SELECT
    Q.*,
    SalesCount = (SELECT COUNT(*) FROM Sales S
        WHERE YEAR(S."Sale Date") = Q.Year AND MONTH(S."Sale Date") = Q.MonthNumber)
FROM Quota Q

And this is the result:

MonthNumber Year       Goal       SalesCount
2           2017       5          1
3           2017       10         2
4           2017       8          2
5           2017       8          0
6           2017       10         0