CREATE EXTERNAL FILE FORMAT (Transact-SQL)

**APPLIES TO:** SQL Server (starting with 2016) Azure SQL Database Azure SQL Data Warehouse Parallel Data Warehouse

Creates an External File Format object defining external data stored in Hadoop, Azure Blob Storage, or Azure Data Lake Store. Creating an external file format is a prerequisite for creating an External Table. By creating an External File Format, you specify the actual layout of the data referenced by an external table.

PolyBase supports the following file formats:

• Delimited Text

• Hive RCFile

• Hive ORC

• Parquet

To create an External Table, see CREATE EXTERNAL TABLE (Transact-SQL).

Transact-SQL Syntax Conventions

Syntax

-- Create an external file format for PARQUET files.  
CREATE EXTERNAL FILE FORMAT file_format_name  
WITH (  
    FORMAT_TYPE = PARQUET  
     [ , DATA_COMPRESSION = {  
        'org.apache.hadoop.io.compress.SnappyCodec'  
      | 'org.apache.hadoop.io.compress.GzipCodec'      }  
    ]);  
  
--Create an external file format for ORC files.  
CREATE EXTERNAL FILE FORMAT file_format_name  
WITH (  
    FORMAT_TYPE = ORC  
     [ , DATA_COMPRESSION = {  
        'org.apache.hadoop.io.compress.SnappyCodec'  
      | 'org.apache.hadoop.io.compress.DefaultCodec'      }  
    ]);  
  
--Create an external file format for RCFILE.  
CREATE EXTERNAL FILE FORMAT file_format_name  
WITH (  
    FORMAT_TYPE = RCFILE,  
    SERDE_METHOD = {  
        'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe'  
      | 'org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe'  
    }  
    [ , DATA_COMPRESSION = 'org.apache.hadoop.io.compress.DefaultCodec' ]);  
  
--Create an external file format for DELIMITED TEXT files.  
CREATE EXTERNAL FILE FORMAT file_format_name  
WITH (  
    FORMAT_TYPE = DELIMITEDTEXT  
    [ , FORMAT_OPTIONS ( <format_options> [ ,...n  ] ) ]  
    [ , DATA_COMPRESSION = {  
           'org.apache.hadoop.io.compress.GzipCodec'  
         | 'org.apache.hadoop.io.compress.DefaultCodec'  
        }  
     ]);  
  
<format_options> ::=  
{  
    FIELD_TERMINATOR = field_terminator  
    | STRING_DELIMITER = string_delimiter 
    | First_Row = integer -- ONLY AVAILABLE SQL DW
    | DATE_FORMAT = datetime_format  
    | USE_TYPE_DEFAULT = { TRUE | FALSE } 
    | Encoding = {'UTF8' | 'UTF16'} 
}  

Arguments

file_format_name
Specifies a name for the external file format.

FORMAT_TYPE = [ PARQUET | ORC | RCFILE | PARQUET] Specifies the format of the external data.

• PARQUET Specifies a Parquet format.

• ORC
  Specifies an Optimized Row Columnar (ORC) format. This option requires Hive version 0.11 or higher on the external Hadoop cluster. In Hadoop, the ORC file format offers better compression and performance than the RCFILE file format.

• RCFILE (in combination with SERDE_METHOD = SERDE_method) Specifies a Record Columnar file format (RcFile). This option requires you to specify a Hive Serializer and Deserializer (SerDe) method. This requirement is the same if you use Hive/HiveQL in Hadoop to query RC files. Note, the SerDe method is case-sensitive.

Examples of specifying RCFile with the two SerDe methods that PolyBase supports.

-   FORMAT_TYPE = RCFILE, SERDE_METHOD = 'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe'

-   FORMAT_TYPE = RCFILE, SERDE_METHOD = 'org.apache.hadoop.hive.serde2.columnar.ColumnarSerDe'

• DELIMITEDTEXT Specifies a text format with column delimiters, also called field terminators.

FIELD_TERMINATOR = field_terminator
Applies only to delimited text files. The field terminator specifies one or more characters that mark the end of each field (column) in the text-delimited file. The default is the pipe character ꞌ|ꞌ. For guaranteed support, we recommend using one or more ascii characters.

Examples:

• FIELD_TERMINATOR = ‘|’

• FIELD_TERMINATOR = ’ ’

• FIELD_TERMINATOR = ꞌ

• FIELD_TERMINATOR = ‘_|’

STRING_DELIMITER = string_delimiter
Specifies the field terminator for data of type string in the text-delimited file. The string delimiter is one or more characters in length and is enclosed with single quotes. The default is the empty string "". For guaranteed support, we recommend using one or more ascii characters.

Examples:

• STRING_DELIMITER = ‘"’

• STRING_DELIMITER = ‘0x22’ – Double quote hex

• STRING_DELIMITER = ’*’

• STRING_DELIMITER = ꞌ,ꞌ

• STRING_DELIMITER = ‘0x7E0x7E’ – Two tildes (for example, ~~)

FIRST_ROW = First_row_int
Specifies the row number that is read first in all files during a PolyBase load. This parameter can take values 1-15. If the value is set to two, the first row in every file (header row) is skipped when the data is loaded. Rows are skipped based on the existence of row terminators (/r/n, /r, /n). When this option is used for export, rows are added to the data to make sure the file can be read with no data loss. If the value is set to >2, the first row exported is the Column names of the external table.

DATE_FORMAT = datetime_format
Specifies a custom format for all date and time data that might appear in a delimited text file. If the source file uses default datetime formats, this option isn’t necessary. Only one custom datetime format is allowed per file. You can’t specify more than one custom datetime formats per file. However, you can use more than one datetime formats if each one is the default format for its respective data type in the external table definition.

PolyBase only uses the custom date format for importing the data. It doesn’t use the custom format for writing data to an external file.

When DATE_FORMAT isn’t specified or is the empty string, PolyBase uses the following default formats:

• DateTime: ‘yyyy-MM-dd HH:mm:ss’

• SmallDateTime: ‘yyyy-MM-dd HH:mm’

• Date: ‘yyyy-MM-dd’

• DateTime2: ‘yyyy-MM-dd HH:mm:ss’

• DateTimeOffset: ‘yyyy-MM-dd HH:mm:ss’

• Time: ‘HH:mm:ss’

Example date formats are in the following table:

Notes about the table:

• Year, month, and day can have a variety of formats and orders. The table shows only the ymd format. Month can have one or two digits, or three characters. Day can have one or two digits. Year can have two or four digits.

• Milliseconds (fffffff) are not required.

• Am, pm (tt) isn’t required. The default is AM.

All supported date formats:

Details:

• To separate month, day and year values, you can use ‘–’, ‘/’, or ‘.’. For simplicity, the table uses only the ’ – ’ separator.

• To specify the month as text, use three or more characters. Months with one or two characters are interpreted as a number.

• To separate time values, use the ‘:’ symbol.

• Letters enclosed in square brackets are optional.

• The letters ‘tt’ designate [AM|PM|am|pm]. AM is the default. When ‘tt’ is specified, the hour value (hh) must be in the range of 0 to 12.

• The letters ‘zzz’ designate the time zone offset for the system’s current time zone in the format {+|-}HH:ss].

USE_TYPE_DEFAULT = { TRUE | FALSE }
Specifies how to handle missing values in delimited text files when PolyBase retrieves data from the text file.

TRUE
When retrieving data from the text file, store each missing value by using the default value for the data type of the corresponding column in the external table definition. For example, replace a missing value with:

• 0 if the column is defined as a numeric column.

• Empty string "" if the column is a string column.

• 1900-01-01 if the column is a date column.

FALSE
Store all missing values as NULL. Any NULL values that are stored by using the word NULL in the delimited text file are imported as the string ‘NULL’.

Encoding = {’UTF8’ | ‘UTF16’}
In Azure SQL Data Warehouse, PolyBase can read UTF8 and UTF16-LE encoded delimited text files. In SQL Server and PDW, PolyBase doesn’t support reading UTF16 encoded files.

DATA_COMPRESSION = data_compression_method
Specifies the data compression method for the external data. When DATA_COMPRESSION isn’t specified, the default is uncompressed data. To work properly, Gzip compressed files must have the “.gz” file extension.

The DELIMITEDTEXT format type supports these compression methods:

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.DefaultCodec’

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.GzipCodec’

The RCFILE format type supports this compression method:

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.DefaultCodec’

The ORC file format type supports these compression methods:

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.DefaultCodec’

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.SnappyCodec’

The PARQUET file format type supports the following compression methods:

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.GzipCodec’

• DATA COMPRESSION = ‘org.apache.hadoop.io.compress.SnappyCodec’

Permissions

Requires ALTER ANY EXTERNAL FILE FORMAT permission.

General Remarks

The external file format is database-scoped in SQL Server and SQL Server SQL Data Warehouse It is server-scoped in SQL Server SQL Data Warehouse Parallel Data Warehouse

The format options are all optional and only apply to delimited text files.

When the data is stored in one of the compressed formats, PolyBase first decompresses the data before returning the data records.

Limitations and Restrictions

The row delimiter in delimited-text files must be supported by Hadoop’s LineRecordReader. That is, it must be either ‘,’‘, or’’. These delimiters are not user-configurable.

The combinations of supported SerDe methods with RCFiles, and the supported data compression methods are listed previously in this article. Not all combinations are supported.

The maximum number of concurrent PolyBase queries is 32. When 32 concurrent queries are running, each query can read a maximum of 33,000 files from the external file location. The root folder and each subfolder also count as a file. If the degree of concurrency is less than 32, the external file location can contain more than 33,000 files.

Because of the limitation on number of files in the external table, we recommend storing less than 30,000 files in the root and subfolders of the external file location. Also, we recommend keeping the number of subfolders under the root directory to a small number. When too many files are referenced, a Java Virtual Machine out-of-memory exception might occur.

When exporting data to Hadoop or Azure Blob Storage via PolyBase, only the data is exported, not the column names(metadata) as defined in the CREATE EXTERNAL TABLE command.

Locking

Takes a shared lock on the EXTERNAL FILE FORMAT object.

Performance

Using compressed files always comes with the tradeoff between transferring less data between the external data source and SQL Server while increasing the CPU usage to compress and decompress the data.

Gzip compressed text files are not splittable. To improve performance for Gzip compressed text files, we recommend generating multiple files that are all stored in the same directory within the external data source. This file structure allows PolyBase to read and decompress the data faster by using multiple reader and decompression processes. The ideal number of compressed files is the maximum number of data reader processes per compute node. In SQL Server and SQL Server Parallel Data Warehouse the maximum number of data reader processes is 8 per node except Azure SQL Data Warehouse Gen2 which is 20 readers per node. In SQL Server Parallel Data Warehouse SQL Data Warehouse the maximum number of data reader processes per node varies by SLO. See Azure SQL Data Warehouse loading patterns and strategies for details.

Examples

A. Create a DELIMITEDTEXT external file format

This example creates an external file format named textdelimited1 for a text-delimited file. The options listed for FORMAT_OPTIONS specify that the fields in the file should be separated using a pipe character ‘|’. The text file is also compressed with the Gzip codec. If DATA_COMPRESSION isn’t specified, the text file is uncompressed.

For a delimited text file, the data compression method can either be the default Codec, ‘org.apache.hadoop.io.compress.DefaultCodec’, or the Gzip Codec, ‘org.apache.hadoop.io.compress.GzipCodec’.

CREATE EXTERNAL FILE FORMAT textdelimited1  
WITH (  
    FORMAT_TYPE = DELIMITEDTEXT,  
    FORMAT_OPTIONS (  
        FIELD_TERMINATOR = '|',  
        DATE_FORMAT = 'MM/dd/yyyy' ),  
    DATA_COMPRESSION = 'org.apache.hadoop.io.compress.GzipCodec'
);  

B. Create an RCFile external file format

This example creates an external file format for a RCFile that uses the serialization/deserialization method org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe. It also specifies to use the Default Codec for the data compression method. If DATA_COMPRESSION isn’t specified, the default is no compression.

CREATE EXTERNAL FILE FORMAT rcfile1  
WITH (  
    FORMAT_TYPE = RCFILE,  
    SERDE_METHOD = 'org.apache.hadoop.hive.serde2.columnar.LazyBinaryColumnarSerDe',  
    DATA_COMPRESSION = 'org.apache.hadoop.io.compress.DefaultCodec'  
);  

C. Create an ORC external file format

This example creates an external file format for an ORC file that compresses the data with the org.apache.io.compress.SnappyCodec data compression method. If DATA_COMPRESSION isn’t specified, the default is no compression.

CREATE EXTERNAL FILE FORMAT orcfile1  
WITH (  
    FORMAT_TYPE = ORC,  
    DATA_COMPRESSION = 'org.apache.hadoop.io.compress.SnappyCodec'  
);  

D. Create a PARQUET external file format

This example creates an external file format for a Parquet file that compresses the data with the org.apache.io.compress.SnappyCodec data compression method. If DATA_COMPRESSION isn’t specified, the default is no compression.

CREATE EXTERNAL FILE FORMAT parquetfile1  
WITH (  
    FORMAT_TYPE = PARQUET,  
    DATA_COMPRESSION = 'org.apache.hadoop.io.compress.SnappyCodec'  
);  

E. Create a Delimited Text File Skipping Header Row (Azure SQL DW Only)

This example creates an external file format for CSV file with a single header row.

CREATE EXTERNAL FILE FORMAT skipHeader_CSV
WITH (FORMAT_TYPE = DELIMITEDTEXT,
      FORMAT_OPTIONS(
          FIELD_TERMINATOR = ',',
          STRING_DELIMITER = '"',
          FIRST_ROW = 2, 
          USE_TYPE_DEFAULT = True)
)

See Also

CREATE EXTERNAL DATA SOURCE (Transact-SQL)
CREATE EXTERNAL TABLE (Transact-SQL)
CREATE EXTERNAL TABLE AS SELECT (Transact-SQL)
CREATE TABLE AS SELECT (Azure SQL Data Warehouse)
sys.external_file_formats (Transact-SQL)