CREATE EXTERNAL TABLE tablename (column_spec) LOCATION ( 'gphdfs://location') FORMAT 'PARQUET' 

The location can be an Parquet file or a directory containing a set of Parquet files. For the file name you can specify the wildcard character * to match any number of characters. If the location specifies multiple files when reading Parquet files, Greenplum Database uses the schema in the first file that is read as the schema for the other files.

The following table lists how Greenplum database converts the Parquet data type if the Parquet schema definition does not contain an annotation.

The gphdfs protocol considers Parquet schema annotations for these cases. Otherwise, data conversion is based on the parquet schema primitive type :

When reading Parquet type group, the gphdfs protocol converts the group data into an XML document.

This schema contains a required group with the name inner.

message test {
    required byte_array binary_field;
    required int64 int64_field;
    required group inner {
       int32 age;
       required boolean test;
       required byte_array name (UTF8);
       } 
    };

This how a single row of the group data would be converted to XML.

<inner type="group">
  <age type="int">50</age>
  <test type="boolean">true</test>
  <name type="string">fred</name>
</inner>

This example schema contains a repeated group with the name inner.

message test {
    required byte_array binary_field;
    required int64 int64_field;
    repeated group inner {
       int32 age;
       required boolean test;
       required byte_array name (UTF8);
       } 
    };

For a repeated group, the Parquet file can contain multiple sets of the group data in a single row. For the example schema, the data for the inner group is converted into XML data.

This is sample output if the data in the Parquet file contained two sets of data for the inner group.

<inner type="repeated">
  <inner type="group">
    <age type="int">50</age>
    <test type="boolean">true</test>
    <name type="string">fred</name>
  </inner>
  <inner>
    <age type="int">23</age>
    <test type="boolean">false</test>
    <name type="string">sam</name>
  </inner>
</inner>

For writable external tables, you can add parameters after the file specified in the location. You add parameters with the http query string syntax that starts with ? and & between field and value pairs.

When creating the Parquet schema from a Greenplum Database table definition, the schema is generated based on the column data types and

A simple example of a Greenplum Database table definition and the Parquet schema generated by the gphdfs protocol.

An example external table definition for a Parquet file.

CREATE WRITABLE EXTERNAL TABLE films (
   code char(5), 
   title varchar(40),
   id integer,
   date_prod date, 
   subtitle boolean
) LOCATION ( 'gphdfs://my-films') FORMAT 'PARQUET' ;

This is the Parquet schema for the Parquet file my-films generated by the gphdfs protocol.

message films {
    optional byte_array code;
    optional byte_array title (utf8);
    optional int32 id;
    optional binary date_prod (utf8);
    optional byte_array(3) flba_field;
    optional boolean subtitle;
    };

• For writable external tables, column definitions in Greenplum Database external table cannot specify NOT NULL to support automatically generating a Parquet schema. When the gphdfs protocol automatically generates a Parquet schema, the gphdfs protocol specifies the field attribute optional to support null in the Parquet schema. Repeated fields can be null in Parquet.
• The gphdfs protocol supports Parquet nested group structures only for readable external files. The nested structures are converted to an XML document.
• Greenplum Database does not have an unsigned int data type. Greenplum Database converts the Parquet unsigned int data type to the next largest Greenplum Database int type. For example, Parquet uint_8 is converted to Greenplum Database int (32 bit).
• Greenplum Database supports any UDT data type or UDT array data type. Greenplum Database attempts to convert the UDT to a sting. If the UDT cannot be converted to a sting, Greenplum Database returns an error.
• The definition of the Interval data type in Parquet is significantly different than the Interval definition in Greenplum Database and cannot be converted. The Parquet Interval data is formatted as bytea.
• The Date data type in Parquet is starts from 1970.1.1, while Date in Greenplum Database starts from 4173 BC, Greenplum Database cannot convert date data types because largest values are different. A similar situation occurs between Timestamp_millis in Parquet and Timestamp in Greenplum Database.