Operation Manual

Understanding Databases

Linking tables

Crystal Reports User’s Guide 495

Subreports and data files

If your primary report is based on Table A, the subreport is based on Table B,

and the records are linked, your primary considerations are as follows:

• The number of subreports that are run by the program is determined by

the index and the selection formula situation in the primary report:

• If Table A is indexed, and if the primary report has a selection formula

that passes down range limit conditions for the indexed field, the

program runs two subreports.

• If Table A is not indexed, or if Table A is indexed but the selection

formula does not pass down range limit conditions for the indexed

field, the program runs 26 subreports.

• The number of records read for each subreport is determined by the

index situation on Table B:

• If you have an index on Table B, the program will read only the

matching records (100) when it runs a subreport.

• If you do not have an index on Table B, the program will always read

every record in Table B (2600) when it runs a subreport.

SQL database considerations

Since indexes are not critical with SQL data, the primary concern with both

linked tables and subreports is whether or not there is a selection formula in

the primary report that puts range limits on Table A. See “Linking data files” on

page 493.

Linked SQL tables

If there are range limit conditions in the selection formula, the program passes

those conditions down to the server.

• If there is a selection formula that puts range limits on Table A, the server

locates the records in Table A that satisfy the selection criteria (2),

matches them up with the appropriate records in Table B (100), and

returns 200 merged records to the Report Engine.

• If there is no selection formula, or if there is a selection formula that does