[GitHub] [arrow-datafusion] alamb opened a new issue, #6758: Improve default output column names

["alamb (via GitHub)" <gi...@apache.org>]

alamb opened a new issue, #6758:
URL: https://github.com/apache/arrow-datafusion/issues/6758

   ### Is your feature request related to a problem or challenge?
   
   The way that DataFusion names the output columns can be quite messy. For example, the query below produces a column named `"FIRST_VALUE(foo.free) PARTITION BY [foo.host] ORDER BY [foo.time DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW + Int64(5) / Int64(12)"` (yes that whole thing)
   
   Arrow requires column names to be distinct strings and DataFusion creates the name based on the content of the expression. 
   
   Here is the entire query
   
   ```sql
   ❯ create table foo(host varchar, free int, time int) as values ('a', 1, 2), ('a', 3, 4);
   0 rows in set. Query took 0.003 seconds.
   ❯ select first_value(free) over (partition by host order by time desc) + 5 / 12 from foo limit 10;
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | FIRST_VALUE(foo.free) PARTITION BY [foo.host] ORDER BY [foo.time DESC NULLS FIRST] RANGE BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW + Int64(5) / Int64(12) |
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------+
   | 3                                                                                                                                                           |
   | 3                                                                                                                                                           |
   +-------------------------------------------------------------------------------------------------------------------------------------------------------------+
   2 rows in set. Query took 0.003 seconds.
   ```
   
   It also means you can't select the same expression without an alias, which while annoying is likely not a critical usecase
   
   ```sql
   ❯ select free / 1, free / 1 from foo;
   Error during planning: Projections require unique expression names but the expression "foo.free / Int64(1)" at position 0 and "foo.free / Int64(1)" at position 1 have the same name. Consider aliasing ("AS") one of them.
   ❯ select free / 1, free / 1 as col2 from foo;
   +---------------------+------+
   | foo.free / Int64(1) | col2 |
   +---------------------+------+
   | 1                   | 1    |
   | 3                   | 3    |
   +---------------------+------+
   ```
   
   ### Describe the solution you'd like
   
   While the output column names can be controlled via adding an explicit alias,  I think it would be good to have a more concise way of naming the default outputs, especially for window functions
   
   Perhaps something like not adding the `OVER` clause's contents so `FIRST_VALUE(foo.free)` in the above example.
   
   If we do this we need to be careful to allow multiple calls to `FIRST_VALUE` with different `OVER` clauses in the same query
   
   ### Describe alternatives you've considered
   
   _No response_
   
   ### Additional context
   
   If we make the names more concise, we will probably need a solution like https://github.com/apache/arrow-datafusion/issues/6543 to ensure they remain unique


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