OpenCSVSerDe for Processing CSV - Amazon Athena

OpenCSVSerDe for Processing CSV

When you create a table from CSV data in Athena, determine what types of values it contains:

  • If data contains values enclosed in double quotes ("), you can use the OpenCSV SerDe to deserialize the values in Athena. In the following sections, note the behavior of this SerDe with STRING data types.

  • If data does not contain values enclosed in double quotes ("), you can omit specifying any SerDe. In this case, Athena uses the default LazySimpleSerDe. For information, see LazySimpleSerDe for CSV, TSV, and Custom-Delimited Files.

CSV SerDe (OpenCSVSerDe)

The OpenCSV SerDe behaves as follows:

  • Converts all column type values to STRING.

  • To recognize data types other than STRING, relies on the Presto parser and converts the values from STRING into those data types if it can recognize them.

  • Uses double quotes (") as the default quote character, and allows you to specify separator, quote, and escape characters, such as:

    WITH SERDEPROPERTIES ("separatorChar" = ",", "quoteChar" = "`", "escapeChar" = "\\" )
  • Cannot escape \t or \n directly. To escape them, use "escapeChar" = "\\". See the example in this topic.

  • Does not support embedded line breaks in CSV files.

  • Does not support empty fields in columns defined as a numeric data type.

Note

When you use Athena with OpenCSVSerDe, the SerDe converts all column types to STRING. Next, the parser in Athena parses the values from STRING into actual types based on what it finds. For example, it parses the values into BOOLEAN, BIGINT, INT, and DOUBLE data types when it can discern them. If the values are in TIMESTAMP in the UNIX format, Athena parses them as TIMESTAMP. If the values are in TIMESTAMP in Hive format, Athena parses them as INT. DATE type values are also parsed as INT.

To further convert columns to the desired type in a table, you can create a view over the table and use CAST to convert to the desired type.

For data types other than STRING, when the parser in Athena can recognize them, this SerDe behaves as follows:

  • Recognizes BOOLEAN, BIGINT, INT, and DOUBLE data types and parses them without changes.

  • Recognizes the TIMESTAMP type if it is specified in the UNIX numeric format, such as 1564610311.

  • Does not support TIMESTAMP in the JDBC-compliant java.sql.Timestamp format, such as "YYYY-MM-DD HH:MM:SS.fffffffff" (9 decimal place precision). If you are processing CSV data from Hive, use the UNIX numeric format.

  • Recognizes the DATE type if it is specified in the UNIX numeric format, such as 1562112000.

  • Does not support DATE in another format. If you are processing CSV data from Hive, use the UNIX numeric format.

Note

For information about using the TIMESTAMP and DATE columns when they are not specified in the UNIX numeric format, see the article When I query a table in Amazon Athena, the TIMESTAMP result is empty in the AWS Knowledge Center.

Example: Using the TIMESTAMP type and DATE type specified in the UNIX numeric format.

Consider the following test data:

"unixvalue creationdate 18276 creationdatetime 1579146280000","18276","1579146280000"

The following statement creates a table in Athena from the specified Amazon S3 bucket location.

CREATE EXTERNAL TABLE IF NOT EXISTS testtimestamp1( `profile_id` string, `creationdate` date, `creationdatetime` timestamp ) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde' LOCATION 's3://<location>'

Next, run the following query:

select * from testtimestamp1

The query returns the following result, showing the date and time data:

profile_id creationdate creationdatetime 1 unixvalue creationdate 18276 creationdatetime 1579146280000 2020-01-15 2020-01-16 03:44:40.000

Example: Escaping \t or \n

Consider the following test data:

" \\t\\t\\n 123 \\t\\t\\n ",abc " 456 ",xyz

The following statement creates a table in Athena, specifying that "escapeChar" = "\\".

CREATE EXTERNAL TABLE test1 ( f1 string, s2 string) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde' WITH SERDEPROPERTIES ("separatorChar" = ",", "escapeChar" = "\\") LOCATION 's3://user-test-region/dataset/test1/'

Next, run the following query:

select * from test1;

It returns this result, correctly escaping \t or \n:

f1 s2 \t\t\n 123 \t\t\n abc 456 xyz

SerDe Name

CSV SerDe

Library Name

To use this SerDe, specify its fully qualified class name in ROW FORMAT. Also specify the delimiters inside SERDEPROPERTIES, as follows:

... ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde' WITH SERDEPROPERTIES ( "separatorChar" = ",", "quoteChar" = "`", "escapeChar" = "\\" )

Example

This example presumes data in CSV saved in s3://mybucket/mycsv/ with the following contents:

"a1","a2","a3","a4" "1","2","abc","def" "a","a1","abc3","ab4"

Use a CREATE TABLE statement to create an Athena table based on the data, and reference the OpenCSVSerDe class in ROW FORMAT, also specifying SerDe properties for character separator, quote character, and escape character, as follows:

CREATE EXTERNAL TABLE myopencsvtable ( col1 string, col2 string, col3 string, col4 string ) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.OpenCSVSerde' WITH SERDEPROPERTIES ( 'separatorChar' = ',', 'quoteChar' = '"', 'escapeChar' = '\\' ) STORED AS TEXTFILE LOCATION 's3://location/of/csv/';

Query all values in the table:

SELECT * FROM myopencsvtable;

The query returns the following values:

col1 col2 col3 col4 ----------------------------- a1 a2 a3 a4 1 2 abc def a a1 abc3 ab4
Note

The flight table data comes from Flights provided by US Department of Transportation, Bureau of Transportation Statistics. Desaturated from original.