Project: Apache Spark (App Definition and Development / Streaming & Messaging)
File: sql-ref-syntax-qry-select-transform.md

layout: global title: TRANSFORM displayTitle: TRANSFORM license: | Licensed to the Apache Software Foundation (ASF) under one or more contributor license agreements. See the NOTICE file distributed with this work for additional information regarding copyright ownership. The ASF licenses this file to You under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0 Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License. The `TRANSFORM` clause is used to specify a Hive-style transform query specification to transform the inputs by running a user-specified command or script. Spark's script transform supports two modes: Hive support disabled: Spark script transform can run with `spark.sql.catalogImplementation=in-memory` or without `SparkSession.builder.enableHiveSupport()`. In this case, now Spark only uses the script transform with `ROW FORMAT DELIMITED` and treats all values passed to the script as strings. Hive support enabled: When Spark is run with `spark.sql.catalogImplementation=hive` or Spark SQL is started with `SparkSession.builder.enableHiveSupport()`, Spark can use the script transform with both Hive SerDe and `ROW FORMAT DELIMITED`. ```sql SELECT TRANSFORM ( expression [ , ... ] ) [ ROW FORMAT row_format ] [ RECORDWRITER recordwriterclass ] USING commandorscript [ AS ( [ colname [ coltype ] ] [ , ... ] ) ] [ ROW FORMAT row_format ] [ RECORDREADER recordreaderclass ] ``` expression* Specifies a combination of one or more values, operators and SQL functions that results in a value. row_format* Specifies the row format for input and output. See for more syntax details. RECORDWRITER* Specifies a fully-qualified class name of a custom RecordWriter. The default value is `org.apache.hadoop.hive.ql.exec.TextRecordWriter`. RECORDREADER* Specifies a fully-qualified class name of a custom RecordReader. The default value is `org.apache.hadoop.hive.ql.exec.TextRecordReader`. command_or_script* Specifies a command or a path to script to process data. When Spark uses `ROW FORMAT DELIMITED` format: Spark uses the character `\u0001` as the default field delimiter and this delimiter can be overridden by `FIELDS TERMINATED BY`. Spark uses the character `\n` as the default line delimiter and this delimiter can be overridden by `LINES TERMINATED BY`. Spark uses a string `\N` as the default `NULL` value in order to differentiate `NULL` values from the literal string `NULL`. This delimiter can be overridden by `NULL DEFINED AS`. Spark casts all columns to `STRING` and combines columns by tabs before feeding to the user

For complex types such as `ARRAY`/`MAP`/`STRUCT`, Spark uses `to_json` casts it to an input `JSON` string and uses `from_json` to convert the result output `JSON` string to `ARRAY`/`MAP`/`STRUCT` data. `COLLECTION ITEMS TERMINATED BY` and `MAP KEYS TERMINATED BY` are delimiters to split complex data such as `ARRAY`/`MAP`/`STRUCT`, Spark uses `tojson` and `fromjson` to handle complex data types with `JSON` format. So `COLLECTION ITEMS TERMINATED BY` and `MAP KEYS TERMINATED BY` won't work in default row format. The standard output of the user script is treated as tab-separated `STRING` columns. Any cell containing only a string `\N` is re-interpreted as a literal `NULL` value, and then the resulting `STRING` column will be cast to the data types specified in `col_type`. If the actual number of output columns is less than the number of specified output columns, additional output columns will be filled with `NULL`. For example: ``` output tabs: 1, 2 output columns: A: INT, B INT, C: INT result: ++++ | a| b| c| ++++ | 1| 2| NULL| ++++ ``` If the actual number of output columns is more than the number of specified output columns, the output columns only select the corresponding columns, and the remaining part will be discarded. For example, if the output has three tabs and there are only two output columns: ``` output tabs: 1, 2, 3 output columns: A: INT, B INT result: +++ | a| b| +++ | 1| 2| +++ ``` If there is no `AS` clause after `USING my_script`, the output schema is `key: STRING, value: STRING`. The `key` column contains all the characters before the first tab and the `value` column contains the remaining characters after the first tab. If there are no tabs, Spark returns the `NULL` value. For example: ``` output tabs: 1, 2, 3 output columns: result: +--+-+ | key| value| +--+-+ | 1| 2| +--+-+ output tabs: 1, 2 output columns: result: +--+-+ | key| value| +--+-+ | 1| NULL| +--+-+ ``` When Hive support is enabled and Hive SerDe mode is used: Spark uses the Hive SerDe `org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe` by default, so columns are cast to `STRING` and combined by tabs before feeding to the user script. All literal `NULL` values are converted to a string `\N` in order to differentiate literal `NULL` values from the literal string `NULL`. The standard output of the user script is treated as tab-separated `STRING` columns, any cell containing only a string `\N` is re-interpreted as a `NULL` value, and then the resulting STRING column will be cast to the data type specified in `col_type`. If the actual number of output columns is less than the number of specified output columns, additional output columns will be filled with

If the actual number of output columns is more than the number of specified output columns, the output columns only select the corresponding columns, and the remaining part will be discarded. If there is no `AS` clause after `USING my_script`, the output schema is `key: STRING, value: STRING`. The `key` column contains all the characters before the first tab and the `value` column contains the remaining characters after the first tab. If there is no tab, Spark returns the `NULL` value. These defaults can be overridden with `ROW FORMAT SERDE` or `ROW FORMAT DELIMITED`. ```sql CREATE TABLE person (zip_code INT, name STRING, age INT); INSERT INTO person VALUES (94588, 'Zen Hui', 50), (94588, 'Dan Li', 18), (94588, 'Anil K', 27), (94588, 'John V', NULL), (94511, 'David K', 42), (94511, 'Aryan B.', 18), (94511, 'Lalit B.', NULL); -- With specified output without data type SELECT TRANSFORM(zip_code, name, age) USING 'cat' AS (a, b, c) FROM person WHERE zip_code > 94511; +-++--+ | a | b| c| +-++--+ | 94588| Anil K| 27| | 94588| John V| NULL| | 94588| Zen Hui| 50| | 94588| Dan Li| 18| +-++--+ -- With specified output with data type SELECT TRANSFORM(zip_code, name, age) USING 'cat' AS (a STRING, b STRING, c STRING) FROM person WHERE zip_code > 94511; +-++--+ | a | b| c| +-++--+ | 94588| Anil K| 27| | 94588| John V| NULL| | 94588| Zen Hui| 50| | 94588| Dan Li| 18| +-++--+ -- Using ROW FORMAT DELIMITED SELECT TRANSFORM(name, age) ROW FORMAT DELIMITED FIELDS TERMINATED BY ',' LINES TERMINATED BY '\n' NULL DEFINED AS 'NULL' USING 'cat' AS (name_age string) ROW FORMAT DELIMITED FIELDS TERMINATED BY '@' LINES TERMINATED BY '\n' NULL DEFINED AS 'NULL' FROM person; ++ | name_age| ++ | Anil K,27| | John V,null| | ryan B.,18| | David K,42| | Zen Hui,50| | Dan Li,18| | Lalit B.,null| ++ -- Using Hive Serde SELECT TRANSFORM(zip_code, name, age) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe' WITH SERDEPROPERTIES ( 'field.delim' = '\t' ) USING 'cat' AS (a STRING, b STRING, c STRING) ROW FORMAT SERDE 'org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe' WITH SERDEPROPERTIES ( 'field.delim' = '\t' ) FROM person WHERE zip_code > 94511; +-++--+ | a | b| c| +-++--+ | 94588| Anil K| 27| | 94588| John V| NULL| | 94588| Zen Hui| 50| | 94588| Dan Li| 18| +-++--+ -- Schema-less mode SELECT TRANSFORM(zip_code, name, age) USING 'cat' FROM person WHERE zip_code > 94500; +-++ | key| value| +-++ | 94588| Anil K 27| | 94588| John V \N| | 94511| Aryan B. 18| | 94511| David K 42| | 94588| Zen Hui 50| | 94588| Dan Li 18| | 94511| Lalit B. \N| +-++ ```