The fields included in a join condition must have compatible datatypes, precisions, and scales. For example, you can join an INT field to a DECIMAL field, but not to a DATETIME or VARCHAR field.
Data Validation Option supports joins on fields with the following datatypes: datetime, numeric, and string. Joins are not allowed on binary/other datatypes.
For an XML data source, only child elements of the selected XML group appear as possible join fields.
You can create multiple join conditions.
If you specify a file list connection and the fields in the join condition are not unique among all files in the file list, the join fails.