An input stream that contains a stream of values representing an instance of an SQL structured type or an SQL distinct type. This interface, used only for custom mapping, is used by the driver behind the scenes, and a programmer never directly invokes SQLInput methods. The reader methods (readLong, readBytes, and so on) provide a way for an implementation of the SQLData interface to read the values in an SQLInput object. And as described in SQLData, calls to reader methods must be made in the order that their corresponding attributes appear in the SQL definition of the type. The method wasNull is used to determine whether the last value read was SQL NULL.

When the method getObject is called with an object of a class implementing the interface SQLData, the JDBC driver calls the method SQLData.getSQLType to determine the SQL type of the user-defined type (UDT) being custom mapped. The driver creates an instance of SQLInput, populating it with the attributes of the UDT. The driver then passes the input stream to the method SQLData.readSQL, which in turn calls the SQLInput reader methods in its implementation for reading the attributes from the input stream.