According to the preferred embodiments, a database relationship constraint is defined for a first column that specifies a set of allowable values for the first column that depend on a set of data values in a second column that may be of a different type than data in the first column. In a first embodiment, a database relationship constraint specifies allowable values for one column in a database table based on one or more data values in a different column in the same database table. In a second embodiment, a database relationship constraint specifies a set of allowable values in a first column based on one or more data values in a second column in a different database table. In both cases, the data in the second column may be of a different type than data in the second column.