Tables can be linked in a report as long as the following criteria are met:
The link fields are both database fields.
The link fields contain similar data.
The link fields are the same length.
The link field in the link to (lookup) table is indexed (PC databases only).
Linking tables is rarely a problem. However, there are some circumstances in which you cannot coordinate data from different tables because the data does not meet the linking criteria.
For example, linking to or from a formula field, or linking two unindexed tables cannot be done in a single report. Subreports must be used.