Oracle Message OCI-19211 - column string, specified as key using DBMS_XMLSTORE.setKeyColumn() , must be of scalar type

ERRORcolumn string, specified as key using DBMS_XMLSTORE.setKeyColumn() , must be of scalar type
CAUSEThe column specified using setKeyColumn() was a non-scalar type column.
ACTIONChange the column specified to be a scalar column in the table