Overlap columns were replaced by multi-segment relationships in DataFlex 11.0 and are obsolete.
Define begin- and end column of an overlap column.
SQL Drivers (SQL Server, DB2 and ODBC)
1 .. Number of columns in the table
DF_FIELD_LENGTH (Integer)
DF_FIELD_OFFSET (Integer)
The Field_Overlap_Start and Field_Overlap_End keywords are used to define an overlap column. An overlap column is a logical column that “overlaps” multiple underlying real columns. The keywords are set to the numbers of the columns that are overlapped.
If we want to define a column at number 5 called My_Overlap starting at column 3 and ending at column 4 (inclusive), we need to place the following lines in the intermediate file:
Field_Number 5
Field_Name My_Overlap
Field_Overlap_Start 3
Field_Overlap_End 4
The lines above will insert a column in the table definition. Column number 5 is a logical column; the original column number 5 and higher will shift one position. Overlaps defined in this way always overlap complete columns.
Please note that the overlap column will be inserted when the column definition is finished at a new field group header, an index group header or the end of the intermediate file. Therefore, the following intermediate file definition will generate two subsequent overlap columns at position 5 and 6. The original column number 5 and higher will have shifted two positions.
Field_Number 5
Field_Name Eventually_Field_6
Field_Overlap_Start 2
Field_Overlap_End 3
Field_Number 5
Field_Name Eventually_Field_5
Field_Overlap_Start 1
Field_Overlap_End 3
The biggest reason to use overlap columns in a DataFlex environment was to define relationships. Up until DataFlex 11 relationships had to be defined from one single column to one single column. Overlap column where used to create multi segment relationships and still comply with the 1 column relationship requirement. With the introduction of VDF11 multi segment relationships are supported. There is no need to define overlap fields for multi segment relationship anymore.