[GitHub] [arrow-datafusion] alamb commented on a change in pull request #422: add output field name rfc

[GitBox <gi...@apache.org>]

alamb commented on a change in pull request #422:
URL: https://github.com/apache/arrow-datafusion/pull/422#discussion_r638965856



##########
File path: docs/rfcs/output-field-name-semantic.md
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@@ -0,0 +1,236 @@
+# Datafusion output field name semantic
+
+Start Date: 2020-05-24
+
+## Summary
+
+Formally specify how Datafusion should construct its output field names based on
+provided user query.
+
+## Motivation
+
+By formalizing the output field name semantic, users will be able to access
+query output using consistent field names.
+
+## Detailed design
+
+The proposed semantic is chosen for the following reasons:
+
+* Ease of implementation, field names can be derived from physical expression
+without having to add extra logic to pass along arbitrary user provided input.
+Users are encouraged to use ALIAS expressions for full field name control.
+* Mostly compatible with Spark’s behavior except literal string handling.
+* Mostly backward compatible with current Datafusion’s behavior other than
+function name cases and parenthesis around operator expressions.
+
+###  Field name rules
+
+* All field names MUST not contain relation qualifier.
+  * Both `SELECT t1.id` and `SELECT id` SHOULD result in field name: `id`
+* Function names MUST be converted to lowercase.
+  * `SELECT AVG(c1)` SHOULD result in field name: `avg(c1)`
+* Literal string MUST not be wrapped with quotes or double quotes.
+  * `SELECT 'foo'` SHOULD result in field name: `foo`
+* Operator expressions MUST be wrapped with parentheses.
+  * `SELECT -2` SHOULD result in field name: `(- 2)`

Review comment:
       Should there really be a space between `-` and `2`?
   
   ```suggestion
     * `SELECT -2` SHOULD result in field name: `(-2)`
   ```




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