Detail – Master Query in Visual Basic
Set status fields of master record based on characteristic of detail records
In this visual basic example let us assume we have two tables in a master/detail relationship. The main table contains Tasks which much be completed. The detail table contains one or more Action Items for each task. The two tables are linked by Task_ID. All Action Items must be completed before the Task is complete. We want to mark the task as done when all the action items have been completed. We have a visual basic AfterUpdate trigger associated with the Completed field in the Action Items form. Here is the code to update the master table (Tasks) when all items are completed for the task.
Private Sub Action_Complete_AfterUpdate()
If Me.Action_Complete=true then
DoCmd.RunSQL (“Update Tasks set Task_Complete=True ” & _
” Where Tasks.Task_ID in ” & _
” (Select Task_ID from Action_Items where Task_ID=” & Me.Task_ID & _
” Having Max(Action_Items.Action_Completed)=-1 ” & _
” Group By Task_ID)”)
DoCmd.RunSql (“Update Tasks set Task_Complete=False ” & _
” where Task_ID=” & Me.Task_ID)
Ok… this is more of an SQL example than a visual basic example. But this is a perfect example of creating a very simple solution to a potentially very complicated task. The key to creating highly maintainable Access databases is to have a consultant who knows both SQL programming and visual basic programming.
Here is the trick to this query… If all the Action_Completed Yes/No fields are true (-1) then the Max of them will be -1. If any are not true (0) then the Max will be 0.
You should have indexes on all table fields mentioned in the SQL statement.
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