Question

I’m trying to write a plain SQL statement for building an Oracle report but I’m stuck at some point. x_request table stores the requests made and different tasks related to specific requests that have been done are stored in x_request_work_log. To summarize the structure of these tables:

X_request

-id  
-name
-requester
-request_date

x_request_work_log

-id
-request_id (foreign key)
-taskId
-start_date
-end_date

Now let’s assume that these tables are filled with sample data as follows:

x_request

id    name      requester    request_date
1     firstReq  John         01/01/2012
2     secondReq Steve        21/01/2012

x_request_work_log

id    requestId    taskId    startDate     endDate
1     1            0         01/01/2012    03/01/2012
2     1            1         04/01/2012    04/01/2012
3     1            2         05/01/2012    15/01/2012
4     2            0         24/01/2012    02/02/2012

The template of my report is as follows:

requestName    timeSpent(task(0))    timeSpent(task(1))     timeSpent(task(2)) 
|          |   |                 |   |                |     |                |

So, that’s where I’m stuck. I need a Sql Select statement that will return each row in the formatted way as described above. How can i retrieve and display the start and end dates of different tasks. Btw timeSpent = endDate(task(x)) – startDate(task(x))

Note: Using different select subqueries for each spent time calculation is not an option due to performance constraints. There must be another way.

Answer 1

It sounds like you just want something like

SELECT r.name request_name,
       SUM( (CASE WHEN l.taskId = 0 
                  THEN l.endDate - l.StartDate
                  ELSE 0
               END) ) task0_time_spent,
       SUM( (CASE WHEN l.taskId = 1 
                  THEN l.endDate - l.StartDate
                  ELSE 0
               END) ) task1_time_spent,
       SUM( (CASE WHEN l.taskId = 2 
                  THEN l.endDate - l.StartDate
                  ELSE 0
               END) ) task2_time_spent
  FROM x_request_work_log l
       JOIN x_request r ON (l.requestId = r.Id)
 GROUP BY r.name

If you happen to be using 11g, you could also use the PIVOT operator.