User`s guide

23.5.7 The Database Expert Links tab
The Database Expert Links tab lets you easily link two or more tables. Choose the Database Expert
from the Database menu to display all current tables; then choose the Links tab to display all current
links.
The easiest way to link database tables is to select Auto Link in the Database Expert Links tab. Auto
Link automatically chooses links for your tables based on common fields in tables or indexed fields (if
your database supports indexed fields).
23.5.8 Linking indexed tables
When you are linking direct-access database tables, you link from a primary table to a field in the lookup
table. The link field in the primary table can be indexed, but does not have to be. The link field in the
lookup table does not have to be indexed, either, unless you aren't using a native driver for your
connection.
In addition, the fields used to link two tables must have the same data type. For example, you can link
a string field in one table to a string field in another table, or a numeric field in one table to a numeric
field in another table, but you cannot link a numeric field in one table to a string field in another table.
• Some DBMS applications allow you to convert the field value to another data type in the index. For
instance, the field in the table can be numeric, while the index converts the field value to a string.
However, if you choose to use that field to link to another table, you must link to a field of the original
data type. You cannot link a string value to a numeric field that has been converted to a string in the
index.
• If you are linking tables from two different ODBC data sources, MS SQL Server and Oracle, for
example, you can only use string fields to link the tables. String fields are stored in databases in the
same manner, regardless of the data source. Other types of values, however, may not be stored
the same way in different data sources, so you cannot link different data sources in Crystal Reports
using anything other than string values.
• When linking direct-access database tables using native drivers (non-SQL), the only join type
available is Left Outer join.
23.5.8.1 Changing the index used in linking
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Understanding Databases