GET_METADATA

返回 Parquet 文件的元数据。元数据包括行组的数量和大小、列名以及有关块和压缩的信息。元数据以 JSON 形式返回。

此函数检查一个文件。Parquet 数据通常跨越单个目录中的多个文件；选择一个。该函数不接受目录名称作为实参。

这是元函数。您必须在顶级 SELECT 语句中调用元函数。

行为类型

易变

语法

GET_METADATA( 'filename' )

参数

filename

Parquet 文件的名称。任何对 COPY 有效的路径都对该函数有效。此函数不对其他格式的文件进行操作。

特权

在 USER 可访问的存储位置上具有 READ 权限的超级用户或非超级用户（请参阅 GRANT（存储位置））。

示例

您必须使用单个文件而不是目录或 glob 调用此函数：

=> SELECT GET_METADATA('/data/emp-row.parquet');
                GET_METADATA
----------------------------------------------------------------------------------------------------
 schema:
required group field_id=-1 spark_schema {
  optional int32 field_id=-1 employeeID;
  optional group field_id=-1 personal {
    optional binary field_id=-1 name (String);
    optional group field_id=-1 address {
      optional binary field_id=-1 street (String);
      optional binary field_id=-1 city (String);
      optional int32 field_id=-1 zipcode;
    }
    optional int32 field_id=-1 taxID;
  }
  optional binary field_id=-1 department (String);
}

 data page version:
  data page v1

 metadata:
{
  "FileName": "/data/emp-row.parquet",
  "FileFormat": "Parquet",
  "Version": "1.0",
  "CreatedBy": "parquet-mr version 1.10.1 (build a89df8f9932b6ef6633d06069e50c9b7970bebd1)",
  "TotalRows": "4",
  "NumberOfRowGroups": "1",
  "NumberOfRealColumns": "3",
  "NumberOfColumns": "7",
  "Columns": [
     { "Id": "0", "Name": "employeeID", "PhysicalType": "INT32", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
     { "Id": "1", "Name": "personal.name", "PhysicalType": "BYTE_ARRAY", "ConvertedType": "UTF8", "LogicalType": {"Type": "String"} },
     { "Id": "2", "Name": "personal.address.street", "PhysicalType": "BYTE_ARRAY", "ConvertedType": "UTF8", "LogicalType": {"Type": "String"} },
     { "Id": "3", "Name": "personal.address.city", "PhysicalType": "BYTE_ARRAY", "ConvertedType": "UTF8", "LogicalType": {"Type": "String"} },
     { "Id": "4", "Name": "personal.address.zipcode", "PhysicalType": "INT32", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
     { "Id": "5", "Name": "personal.taxID", "PhysicalType": "INT32", "ConvertedType": "NONE", "LogicalType": {"Type": "None"} },
     { "Id": "6", "Name": "department", "PhysicalType": "BYTE_ARRAY", "ConvertedType": "UTF8", "LogicalType": {"Type": "String"} }
  ],
  "RowGroups": [
     {
       "Id": "0",  "TotalBytes": "642",  "TotalCompressedBytes": "0",  "Rows": "4",
       "ColumnChunks": [
          {"Id": "0", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "51513", "Min": "17103" },
           "Compression": "SNAPPY", "Encodings": "PLAIN RLE BIT_PACKED ", "UncompressedSize": "67", "CompressedSize": "69" },
          {"Id": "1", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "Sheldon Cooper", "Min": "Howard Wolowitz" },
           "Compression": "SNAPPY", "Encodings": "PLAIN RLE BIT_PACKED ", "UncompressedSize": "142", "CompressedSize": "145" },
          {"Id": "2", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "52 Broad St", "Min": "100 Main St Apt 4A" },
           "Compression": "SNAPPY", "Encodings": "PLAIN RLE BIT_PACKED ", "UncompressedSize": "139", "CompressedSize": "123" },
          {"Id": "3", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "Pasadena", "Min": "Pasadena" },
           "Compression": "SNAPPY", "Encodings": "RLE PLAIN_DICTIONARY BIT_PACKED ", "UncompressedSize": "95", "CompressedSize": "99" },
          {"Id": "4", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "91021", "Min": "91001" },
           "Compression": "SNAPPY", "Encodings": "PLAIN RLE BIT_PACKED ", "UncompressedSize": "68", "CompressedSize": "70" },
          {"Id": "5", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "4", "DistinctValues": "0", "Max": "0", "Min": "0" },
           "Compression": "SNAPPY", "Encodings": "PLAIN RLE BIT_PACKED ", "UncompressedSize": "28", "CompressedSize": "30" },
          {"Id": "6", "Values": "4", "StatsSet": "True", "Stats": {"NumNulls": "0", "DistinctValues": "0", "Max": "Physics", "Min": "Astronomy" },
           "Compression": "SNAPPY", "Encodings": "RLE PLAIN_DICTIONARY BIT_PACKED ", "UncompressedSize": "103", "CompressedSize": "107" }
        ]
     }
  ]
}

(1 row)