If the where condition is on a joined table, will I get duplicated results?

I have three tables, one is tasks which are tasks that factory workers complete by putting them into batches, which is anoth开发者_JAVA百科er table, each task has a batch_id, multiple tasks can have the same batch_id. The third table is the batch_log where all time that someone has worked on a batch is recorded in the form of a unique id, a batch_id, the person's userid, the start_time and the end_time.

Each task has an estimated_recurring time in seconds and an estimated_nonrecurring time in seconds. I'm looking to get the sum of both of those fields grouped by the operation_id which is a field in the tasks table to represent whether it is a laser cutting, deburr, painting, etc task.

The issue is that I only want the tasks that have batches that were in the batch_log during a time_period. Batches have multiple entries in the batch_log table.

Here is what I'm trying:

SELECT 
  operation_id, SUM(t.estimated_nonrecurring + t.estimated_recurring) / 3600 as work_completed
FROM tasks t
INNER JOIN batch_log l on t.batch_id = l.batch_id
WHERE 
  l.start_time BETWEEN DATE("10:00:00") AND DATE(NOW())
AND
  l.time_elapsed < "10:00:00"
GROUP BY t.operation_id

I'm concerned that I will get a higher estimate than is real because multiple entries in the task table can have the same batch.

Because you only want the times based on tasks that were in your batch log file what you posted will definately not work.

Assuming you have 3 tables: Tasks, Batches, and BatchLog.

You'll want this:

SELECT
      SUM(t.estimated_nonrecurring + t.estimated_recurring) / 3600 as work_completed,
      t.OperationID
FROM
      Tasks t
INNER JOIN
       Batches b
ON
       b.BatchID = t.BatchID
INNER JOIN
       BatchLog bl
ON
       bl.BatchID = b.BatchID
WHERE  
  bl.start_time BETWEEN DATE("2011-08-01") AND DATE(NOW())
GROUP BY
       t.OperationID