The constant must be declared before including adodb.inc.php. It is not possible to change the default metatype during a procedure.
ADODB_DEFAULT_METATYPE controls the returned metatype of an unknown field type . The default value for this constant is 'N'.
This constant is useful for example in geometry data types where there is no defined metaType in ADOdb
// Connecting to a postgreSql database DEFINE(ADODB_DEFAULT_METATYPE, 'C'); require "adodb/adodb.inc.php"; $db = NewADOConnection('postgres'); // connection assumed $m = $db->metaType('polygon'); print $m; // Unknown, returns: 'C'