Databases have a poorly standardized but rich set of datatypes. Some
have natural Prolog counterparts, some not. A complete mapping requires
us to define Prolog data-types for SQL types that have no standardized
Prolog counterpart (such as timestamp), the definition of a default
mapping and the possibility to define an alternative mapping for a
specific column. For example, many variations of the SQL DECIMAL
type cannot be mapped to a Prolog integer. Nevertheless, mapping to an
integer may be the proper choice for a specific application.
The Prolog/ODBC interface defines the following Prolog result types
with the indicated default transformation. Different result-types can be
requested using the types(TypeList) option for the
odbc_query/4
and odbc_prepare/5
interfaces.
- atom
- Used as default for the SQL types
char, varchar,
longvarchar, binary, varbinary,
longvarbinary, decimal and numeric.
Can be used for all types.
- string
- SWI-Prolog extended type string. Use the type for special cases where
garbage atoms must be avoided. Can be used for all types.
- codes
- List of character codes. Use this type if the argument must be analysed
or compatibility with Prolog systems that cannot handle infinite-length
atoms is desired. Can be used for all types.
- integer
- Used as default for the SQL types
bit, tinyint,
smallint and integer. Please note that
SWI-Prolog integers are signed 32-bit values, where SQL allows for
unsigned values as well. Can be used for the integral, and decimal
types as well as the types date and timestamp,
which are represented as POSIX time-stamps (seconds after Jan 1, 1970).
- float
- Used as default for the SQL types
real, float
and
double. Can be used for the integral and decimal
types as well as the types date and timestamp,
which are represented as POSIX time-stamps (seconds after Jan 1, 1970).
Representing time this way is compatible to SWI-Prologs time-stamp
handling.
- date
- A Prolog term of the form
date(Year,Month,Day) used as
default for the SQL type date.
- time
- A Prolog term of the form
time(Hour,Minute,Second) used as
default for the SQL type time.
- timestamp
- A Prolog term of the form
timestamp(Year,Month,Day,Hour,Minute,Second,Fraction) used
as default for the SQL type timestamp.
