How to implement a subquery in CR2011 using native formulae?

Question

Hi All, If you look at the following SQL query, we want to have EquipRate based on Current Date for a EquipCode. How can I achieve the same result in Crystal reports designer using native formulas and functions. Thanks for your help. It will help us in not creating a view at the database side.
Select a.EquipRate
From a
Where a.EffectiveDate =
(select Maximum (a.EffectiveDate,b.EquipCode)
  from a, b
   where a.id=b.id)
Thanks

Answer 1

While this is possible, it will be MUCH more efficient to create the view OR to create a Command (SQL Select Statement) in the report to do this.
To do this just in Crystal you could do something like this:
1.  Add Table A.
2.  Add a command that is something like this:
(select  b.EquipCode,
  Maximum (a.EffectiveDate)  as MaxDate
  from a
    inner join b on a.id = b.id
  group by b.EquipCode)
3.  Link the table to the command on EquipCode and EffectiveDate/MaxDate
However, if you have a lot of data, this will be VERY slow because Crystal will pull all of the data into memory and then join the table to the command instead of having the database do the join.
The other "just Crystal" option is to write a single Command that pulls all of the data you need for your report.  If your report has any parameters, you'll want to create them in the Command Editor and use them in the Where clause of the query.  Parameters created in the report can't be "seen" in the Command Editor and using the Select Expert instead of the query itself again means that Crystal will pull all of the data into memory and filter it there instead pushing the filter down to the database.
-Dell