Limit Key Size
The maximum length of a primary key column.
In some ODBC tools, for example, Microsoft Access, the length of the primary key column cannot be larger than a specific value. This property makes the ODBC Driver override the reported length of all the primary key columns. It is especially useful when using the ODBC Driver as a Microsoft Access Linked Data Source.
Setting the LimitKeySize to zero will make the key length revert to the original length.
This property can also be set using the SQLSetConnectAttr method, as shown in the following example:
SQLSetConnectAttr(hdbc, 20001, (SQLPOINTER)128, 0);