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Querying Parquet Metadata

## Parquet Metadata

The `parquet_metadata` function can be used to query the metadata contained within a Parquet file, which reveals various internal details of the Parquet file such as the statistics of the different columns. This can be useful for figuring out what kind of skipping is possible in Parquet files, or even to obtain a quick overview of what the different columns contain:

    SELECT *
    FROM parquet_metadata('test.parquet');

Below is a table of the columns returned by `parquet_metadata`.

Field | Type
--- | ---
file_name | VARCHAR
row_group_id | BIGINT
row_group_num_rows | BIGINT
row_group_num_columns | BIGINT
row_group_bytes | BIGINT
column_id | BIGINT
file_offset | BIGINT
num_values | BIGINT
path_in_schema | VARCHAR
type | VARCHAR
stats_min | VARCHAR
stats_max | VARCHAR
stats_null_count | BIGINT
stats_distinct_count | BIGINT
stats_min_value | VARCHAR
stats_max_value | VARCHAR
compression | VARCHAR
encodings | VARCHAR
index_page_offset | BIGINT
dictionary_page_offset | BIGINT
data_page_offset | BIGINT
total_compressed_size | BIGINT
total_uncompressed_size | BIGINT
key_value_metadata | MAP(BLOB, BLOB)

## Parquet Schema

The `parquet_schema` function can be used to query the internal schema contained within a Parquet file. Note that this is the schema as it is contained within the metadata of the Parquet file. If you want to figure out the column names and types contained within a Parquet file it is easier to use `DESCRIBE`.

Fetch the column names and column types:

    DESCRIBE SELECT * FROM 'test.parquet';

Fetch the internal schema of a Parquet file:

    SELECT *
    FROM parquet_schema('test.parquet');

Below is a table of the columns returned by `parquet_schema`.

Field | Type
--- | ---
file_name | VARCHAR
name | VARCHAR
type | VARCHAR
type_length | VARCHAR
repetition_type | VARCHAR
num_children | BIGINT
converted_type | VARCHAR
scale | BIGINT
precision | BIGINT
field_id | BIGINT
logical_type | VARCHAR

## Parquet File Metadata

The `parquet_file_metadata` function can be used to query file-level metadata such as the format version and the encryption algorithm used:

    SELECT *
    FROM parquet_file_metadata('test.parquet');

Below is a table of the columns returned by `parquet_file_metadata`.

Field | Type
--- | ---
file_name | VARCHAR
created_by | VARCHAR
num_rows | BIGINT
num_row_groups | BIGINT
format_version | BIGINT
encryption_algorithm | VARCHAR
footer_signing_key_metadata | VARCHAR

## Parquet Key-Value Metadata

The `parquet_kv_metadata` function can be used to query custom metadata defined as key-value pairs:

    SELECT *
    FROM parquet_kv_metadata('test.parquet');

Below is a table of the columns returned by `parquet_kv_metadata`.

Field | Type
--- | ---
file_name | VARCHAR
key | BLOB
value | BLOB

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