pg_field_type_oid() returns an integer containing the OID of the base type of the given field_number in the given PostgreSQL result resource.
You can get more information about the field type by querying PostgreSQL's pg_type system table using the OID obtained with this function. The PostgreSQL format_type() function will convert a type OID into an SQL standard type name.
注: If the field uses a PostgreSQL domain (rather than a basic type), it is the OID of the domain's underlying type that is returned, rather than the OID of the domain itself.
PostgreSQL query result resource, returned by pg_query(), pg_query_params() or pg_execute() (among others).
Field number, starting from 0.