ODBC to Jet Data Type Mapping in our Data Access Drivers for Informix

Numeric Data Type Mappings in our Data Access Drivers for Informix

The table below details how the OpenLink data access drivers fetch numeric data from Informix.

The SQL type reported for a SELECT column varies depending on the native Informix type of the column, its precision, and its scale. The C type used to fetch the data is also shown, together with the effect of the JetFix switch.

Changes to the type mappings required to implement the JetFix option are shown in italics.

Table 1. Numeric Data Type Mappings

Precision of C Data Types

The C data type used to fetch a numeric value is determined by the maximum precision supported by the type.

If a numeric type exists which can represent the data to be fetched without loss of precision, then this is used as the preferred fetch type.

If a numeric type capable of supporting the required precision does not exist, then the data is fetched in character form, unless the JetFix switch is on. In this case, the data is fetched using the CTYPE_FLT64 fetch type, which has sufficient range to store the maximum numeric values supported by Informix. However, CTYPE_FLT64 may result in a loss of precision, if the precision of the data to be fetched exceeds 15 decimal digits.

Table 2. Precision of C Data Types

Informix Jetfix Testing

To verify the effect of the +jetfix switch, two tables were created and then linked into Access -- once with JetFix enabled, and once with JetFix disabled.

The first table contained five MONEY columns of various precisions and scales.

The second table was identical except that it used DECIMAL instead of MONEY columns.

The resulting Jet data type mappings as shown in the 'Table Design' view are detailed below:

Table 3. Informix ODBC to Jet Data Type Mapping