Software Platform User guide

program passes down the first condition, retrieves the data set that
satisfies the condition, and then applies the second condition only to the
retrieved data. The rule for AND situations is that the program passes
down whatever conditions it can.
Note:
If all of the conditions in an AND situation can be satisfied on the server
or in the database DLL, the program passes them all down.
• OR situations
{customer.REGION} = "CA" or
{customer.CUSTOMER ID}[3 to 5] = "777")
In this situation, the program also sees that it can pass down the condition
before the Or operator but not the condition after. Since there are records
that can satisfy the second condition without satisfying the first, passing
the first condition down does not make any sense because it will retrieve
an incomplete data set. In other words, even if it retrieves all the data that
satisfies the first condition, it will still have to retrieve all the data in the
table(s) before it can apply the second condition in Report Designer. Thus,
instead of duplicating parts of the data retrieval, the program passes
nothing down. It retrieves all the data and then runs both tests in Report
Designer. The rule for OR situations is that the program either passes
down all the tests, or none of the tests.
Note:
If all the tests in an OR situation can be performed on the server or in the
database DLL, the program passes them all down.
Consideration 2
To make certain the program can use the index on Table A to enhance
performance, make certain:
• There is a selection formula.
• There are range limits in the selection formula on the key (indexed) field
in Table A.
• Use Indexes is selected in the Options dialog box.
Crystal Reports 2008 SP3 User's Guide 675
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Understanding Databases
Linking tables