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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2022/02/26 20:08:46 UTC

[GitHub] [arrow-datafusion] andygrove opened a new issue #1890: Add support for SQL coalesce function

andygrove opened a new issue #1890:
URL: https://github.com/apache/arrow-datafusion/issues/1890


   **Is your feature request related to a problem or challenge? Please describe what you are trying to do.**
   I would like DataFusion to support the `coalesce` SQL function.
   
   Here is the [Postgres documentation](https://www.postgresql.org/docs/8.1/functions-conditional.html) for this function:
   
   ## 9.13.2. COALESCE
   
   ``` sql
   COALESCE(value [, ...])
   ```
   
   The COALESCE function returns the first of its arguments that is not null. Null is returned only if all arguments are null. It is often used to substitute a default value for null values when data is retrieved for display, for example:
   
   ``` sql
   SELECT COALESCE(description, short_description, '(none)') ...
   ```
   
   Like a CASE expression, COALESCE will not evaluate arguments that are not needed to determine the result; that is, arguments to the right of the first non-null argument are not evaluated. This SQL-standard function provides capabilities similar to NVL and IFNULL, which are used in some other database systems.
   
   **Describe the solution you'd like**
   As described above.
   
   **Describe alternatives you've considered**
   None
   
   **Additional context**
   This function is required by some of the queries in the TPC-DS benchmark.
   


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[GitHub] [arrow-datafusion] xudong963 commented on issue #1890: Add support for SQL coalesce function

Posted by GitBox <gi...@apache.org>.
xudong963 commented on issue #1890:
URL: https://github.com/apache/arrow-datafusion/issues/1890#issuecomment-1066052040


   > 2\. Can you please also point me to the TPC-DS benchmarks where `coalesce` is required? I did a quick search but couldn't find any.
   
   Many sqls require `Coalesce`, you can check in https://github.com/Agirish/tpcds


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[GitHub] [arrow-datafusion] msathis commented on issue #1890: Add support for SQL coalesce function

Posted by GitBox <gi...@apache.org>.
msathis commented on issue #1890:
URL: https://github.com/apache/arrow-datafusion/issues/1890#issuecomment-1063886165


   Hi @andygrove, I did basic `coalesce` function in #1969. Right now i convert every argument to `string` and return a `string` from the function well. But I have a few doubts and need your help there :) 
   
   1. What data types do we need to support in `coalesce`? All primitive data types? If yes, can you please point me to a place where this is being done already which i can use it as a reference. 
   2. Can you please also point me to the TPC-DS benchmarks where `coalesce` is required? I did a quick search but couldn't find any.


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[GitHub] [arrow-datafusion] msathis commented on issue #1890: Add support for SQL coalesce function

Posted by GitBox <gi...@apache.org>.
msathis commented on issue #1890:
URL: https://github.com/apache/arrow-datafusion/issues/1890#issuecomment-1056851565


   I can take this up if no one is working on it already. 


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