Question

I have two tables in which I my goal is to create a new column that calculates Calls per hour by simply dividing Calls by Hours. However, first I want to add the hours from table2 to table 1 before doing that calculation, adding the hours for the corresponding Name and Date.

Table1:

Name    Calls     Hours     Date
--------------------------------------
John    50        3         9/10/2012
Paul    25        2         9/10/2012
Cindy   60        3         9/10/2012
David   50        2.5       9/10/2012
John    45        4         9/9/2012
Paul    50        5         9/9/2012
Cindy   20        2         9/9/2012
David   20        2         9/9/2012

Table 2:

Date         Name     Hours     
------------------------------
9/10/2012    John       1
9/10/2012    Paul       2
9/10/2012    Cindy      2
9/9/2012     John       2.5
9/9/2012     Paul       1.5
9/9/2012     Cindy      0.5

Ultimately my desired query output is this:

Name    Calls   TotalHours    CallsPerHour   Date
-----------------------------------------------------
John    50      4             12.5           9/10/2012
Paul    25      4             6.25           9/10/2012
Cindy   60      5             12             9/10/2012
David   50      2.5           20             9/10/2012
John    45      6.5           6.9230         9/9/2012
Paul    50      6.5           7.6923         9/9/2012
Cindy   20      2.5           8              9/9/2012
David   20      2             10             9/9/2012

P.S. Names are unique in db.

Answer 1

Since both tables can have only one row per Name per Date, you don’t need a GROUP BY query. Use LEFT JOIN to accommodate missing Name/Date combinations in TableTwo.

SELECT
    t1.Name, 
    t1.Calls,
    t1.Hours + Nz(t2.Hours,0) AS TotalHours,
    t1.Calls / (t1.Hours + Nz(t2.Hours,0)) AS CallsPerHour,
    t1.Date
FROM
    TableOne AS t1
    LEFT JOIN TableTwo AS t2
    ON
        t1.Name = t2.Name
    AND t1.Date = t2.Date;

Using your revised sample data, this is the result set from that query.

Name   Calls TotalHours     CallsPerHour Date
John      50          4             12.5 9/10/2012
Paul      25          4             6.25 9/10/2012
Cindy     60          5               12 9/10/2012
David     50        2.5               20 9/10/2012
John      45        6.5 6.92307692307692  9/9/2012
Paul      50        6.5 7.69230769230769  9/9/2012
Cindy     20        2.5                8  9/9/2012
David     20          2               10  9/9/2012