Cannot uniquely identify rows in cursor

Error constant SQLE_CANNOT_UNIQUELY_IDENTIFY_ROWS
ODBC 2 State 42000
ODBC 3 State 42000
Severity 16
SQLCODE –295
SQLSTATE 09W05
Sybase error code 311
Probable cause

You opened a UNIQUE cursor on a SELECT statement for which a set of columns uniquely identifying each row cannot be generated. One of the tables may not be defined with a primary key or uniqueness constraint, or the SELECT statement may involve a UNION, INTERSECT, EXCEPT, or GROUP BY.