8. SQL Statements : DESCRIBE INPUT
Valid in: ESQL
The DESCRIBE INPUT statement returns information about the input parameter markers of a prepared statement. (Input parameter markers are denoted by "?" in the prepared statement.)
When there is a direct correspondence to a table column, such as positional mapping or direct comparison, the type of the table column is returned. Otherwise, a best guess of the type based on local context (such as the nearest resolvable operand) is returned.
Note:  Best-guess types are typically returned as nullable. If no type guess is possible because of lack of context, a zero (illegal) type is returned, but the DESCRIBE INPUT operation succeeds.