There are two basic types of SELECT statements: fixed list and varying list.
To process a fixed-list SELECT statement, an SQL descriptor is not necessary.
To process a varying-list SELECT statement, you
must first declare an SQL descriptor area (SQLDA) structure or ALLOCATE an
SQLDA. Both forms of SQL descriptors can be used to pass host
variable input values from an application program to SQL and to receive output
values from SQL. In addition, information about SELECT list expressions can
be returned in a PREPARE or DESCRIBE statement.