Question

I would like to extract some data from three tables in a SQL Server 2005 database. While this can surely be done in code, it seems like this could be done reasonably well in SQL (bonus points for LINQ!).

Basically, I would like to know for each month how many calls and meetings each employee has held with each of our clients. Something like this:

Employee GUID   Customer GUID   Jan calls   Jan mtgs   Feb calls      Feb mtgs...
[a guid]        [another guid]  5           0          7              3

The data is spread across three tables. For simplicity’s sake, let’s just show the relevant columns:

Communications Table

[CommunicationId]  (PK, uniqueidentifier)
[Type]             (nvarchar(1)) ('C' for call, 'M' for meeting, etc.)
[Date]             (datetime)

Person-Communication Table

[PersonId]         (PK, FK, uniqueidentifier) (Can contain GUIDs for employees or clients, see Person Table below)
[CommunicationId]  (PK, FK, uniqueidentifier)

Person Table

[PersonId]         (PK, uniqueidentifier)
[Type]             (nvarchar(1)) ('E' for employee, 'C' for customer)

So, the questions:

1. Can this be done in SQL without horrendous code or big performance problems?
2. If so, how? I’d even settle for a good high-level strategy. I’m guessing pivots will play a big role here (particularly the “Complex PIVOT Example”). DATEPART(MONTH, Date) seems like a good method for partitioning the communications by month along the lines of:

SELECT DATEPART(MONTH, Date), COUNT(*) 
FROM [CommunicationTable]
WHERE DATEPART(YEAR, Date) = '2009'
GROUP BY DATEPART(MONTH, Date)
ORDER BY DATEPART(MONTH, Date)

… which gets me the number of communications in each month in 2009:

1    2871
2    2639
3    3654
4    2751
5    1773
6    2575
7    2906
8    2398
9    2621
10   2638
11   1705
12   2290

Answer 1

Non PIVOT, CASE using syntax:

WITH summary AS (
      SELECT emp.personid AS emp_guid,
             cust.personid AS cust_guid,
             DATEPART(MONTH, ct.date) AS mon, 
             ct.type,
             COUNT(*) AS num_count
        FROM COMMUNICATIONTABLE ct
   LEFT JOIN PERSON_COMMUNICATION pc ON pc.communicationid = ct.communicationid
        JOIN PERSON emp ON emp.personid = pc.personid
                       AND emp.type = 'E'
        JOIN PERSON cust ON cust.personid = p.personid
                        AND cust.type = 'C'
       WHERE ct.date BETWEEN '2009-01-01' AND '2009-12-31'
    GROUP BY emp.personid, cust.personid, DATEPART(MONTH, ct.ate), ct.type)
SELECT s.emp_guid,
       s.cust_guid,
       MAX(CASE WHEN s.mon = 1 AND s.type = 'C' THEN s.num_count ELSE 0 END) AS "Jan calls",
       MAX(CASE WHEN s.mon = 1 AND s.type = 'M' THEN s.num_count ELSE 0 END) AS "Jan mtgs",
       ... --Copy/Paste two lines, update the month check... and the col alias
  FROM summary s
GROUP BY s.emp_guid, s.cust_guid

Use WHERE ct.date BETWEEN '2009-01-01' AND '2009-12-31' because WHERE DATEPART(YEAR, Date) = '2009' can’t use an index if one exists on the date column.