Impedance

In some cases, SQL and C have equivalent data types and a C data type can be substituted for an SQL data type (for example, int and mi_integer); but in other cases, they do not have equivalent types. This mismatch between the C and SQL type systems is known as impedance. The C code in user-defined routines must map the arguments of the routine and return values between the two type systems, as is the case where the SQL type decimal is mapped to the C type double.