Put column values into a system-descriptor area

When you create a SELECT statement dynamically, you cannot use the INTO host_var clause of FETCH because you cannot name the host variables in the prepared statement. To fetch column values into a system-descriptor area, use the USING SQL DESCRIPTOR clause of FETCH instead of the INTO clause. The FETCH...USING SQL DESCRIPTOR statement puts each column value into the DATA field of its item descriptor.

Use of the FETCH...USING SQL DESCRIPTOR statement assumes the existence of a cursor associated with the prepared statement. You must always use a cursor for SELECT statements and cursor functions (EXECUTE FUNCTION statements that return multiple rows). However, if the SELECT (or EXECUTE FUNCTION) returns only one row, you can omit the cursor and retrieve the column values into a system-descriptor area with the EXECUTE...INTO SQL DESCRIPTOR statement.
Important: If you execute a SELECT statement or user-defined function that returns more than one row and do not associate the statement with a cursor, your program generates a runtime error. When you associate a singleton SELECT (or EXECUTE FUNCTION) statement with a cursor, Informix® ESQL/C does not generate an error. Therefore, it is a good practice to always associate a dynamic SELECT or EXECUTE FUNCTION statement with a cursor and to use a FETCH...USING SQL DESCRIPTOR statement to retrieve the column values from this cursor into the system-descriptor area.

When the column values are in the system-descriptor area, you can use the GET DESCRIPTOR statement to transfer these values from their DATA fields to the appropriate host variables. You must use the LENGTH and TYPE fields to determine, at run time, the data types for these host variables. You might need to perform data type or length conversions between the SQL data types in the TYPE fields and the Informix® ESQL/C data types that are needed for host variables that hold the return value.

For more information about how to execute SELECT statements dynamically, see Handling an unknown select list. For more information about how to execute user-defined functions dynamically, see Handling unknown return values.