AngersZhuuuu commented on a change in pull request #31010: URL: https://github.com/apache/spark/pull/31010#discussion_r615589222
########## File path: docs/sql-ref-syntax-qry-select-transform.md ########## @@ -0,0 +1,242 @@ +--- +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. +--- + +### Description + +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. + +### Syntax + +```sql +SELECT TRANSFORM ( expression [ , ... ] ) + [ ROW FORMAT row_format ] + [ RECORDWRITER record_writer_class ] + USING command_or_script [ AS ( [ col_name [ col_type ] ] [ , ... ] ) ] + [ ROW FORMAT row_format ] + [ RECORDREADER record_reader_class ] + +row_format: + : SERDE serde_class [ WITH SERDEPROPERTIES (k1=v1, k2=v2, ... ) ] + | DELIMITED [ FIELDS TERMINATED BY fields_terminated_char [ ESCAPED BY escaped_char ] ] + [ COLLECTION ITEMS TERMINATED BY collection_items_terminated_char ] + [ MAP KEYS TERMINATED BY map_key_terminated_char ] + [ LINES TERMINATED BY row_terminated_char ] + [ NULL DEFINED AS null_char ] +``` + +### Parameters + +* **expression** + + Specifies a combination of one or more values, operators and SQL functions that results in a value. + +* **row_format** + + Spark uses the `SERDE` clause to specify a custom SerDe for one table. Otherwise, use the `DELIMITED` clause to use the native SerDe and specify the delimiter, escape character, null character and so on. + +* **SERDE** + + Specifies a custom SerDe for one table. + +* **serde_class** + + Specifies a fully-qualified class name of a custom SerDe. + +* **DELIMITED** + + The `DELIMITED` clause can be used to specify the native SerDe and state the delimiter, escape character, null character and so on. + +* **FIELDS TERMINATED BY** + + Used to define a column separator. + +* **COLLECTION ITEMS TERMINATED BY** + + Used to define a collection item separator. + +* **MAP KEYS TERMINATED BY** + + Used to define a map key separator. + +* **LINES TERMINATED BY** + + Used to define a row separator. + +* **NULL DEFINED AS** + + Used to define the specific value for NULL. + +* **ESCAPED BY** + + Used for escape mechanism. + +* **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. + +### SerDe behavior + +Spark uses Hive Serde `org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe` by default, columns will be casted +to `STRING` and combined by tabs before feeding to the user script. All `NULL` values will be converted +to the literal string `"\N"` in order to differentiate `NULL` values from empty strings. The standard output of the +user script will be treated as TAB-separated STRING columns, any cell containing only `"\N"` will be re-interpreted +as a `NULL`, and then the resulting STRING column will be cast to the data type specified in the table declaration +in the usual way. If the actual number of output columns is less than the number of specified output columns, +insufficient output columns will be supplemented with `NULL`. If the actual number of output columns is more than the +number of specified output columns, the output columns will only select the corresponding columns and the remaining part +will be discarded. If there is no `AS` clause after `USING my_script`, Spark assumes that the output of the script contains 2 parts: + + 1. key: which is before the first tab. + 2. value: which is the rest after the first tab. + +If there is no enough tab, Spark will return `NULL` value in `SERDE` mode or throw `ArrayOutOfBoundsException` in `DELIMITED` mode. Review comment: Have been fixed in https://github.com/apache/spark/pull/29421/files -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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