[jira] [Commented] (IMPALA-7741) Functions nvl2(), decode(), nullif() not listed in _impala_builtins

["Paul Rogers (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/IMPALA-7741?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16659759#comment-16659759 ] 

Paul Rogers commented on IMPALA-7741:
-------------------------------------

{{gen_builtins_catalog.py}} generates {{ScalarBuiltins.java}} from information in {{impala_functions.py}}. This presents a difficulty. {{impala_functions.py}} lists functions implemented in the backend. However, the FE rewrites multiple functions out of existence, so no BE implementation is necessary.

{{impala_functions.py}} divides functions into two categories: {{visible_functions}} and {{invisible_functions}}. Perhaps the cleanest solution is to add a third category: {{fe_only_functions}} to describe those available to the user, but which happen to be rewritten away by the FE.

{{gen_builtins_catalog.py}} would then combine the existing {{visible_functions}} with the new {{fe_only_functions}} to create the final set of functions in {{ScalarBuiltins.java}}. The two existing categories would continue to drive the BE code generation.

> Functions nvl2(), decode(), nullif() not listed in _impala_builtins
> -------------------------------------------------------------------
>
>                 Key: IMPALA-7741
>                 URL: https://issues.apache.org/jira/browse/IMPALA-7741
>             Project: IMPALA
>          Issue Type: Improvement
>    Affects Versions: Impala 3.0
>            Reporter: Paul Rogers
>            Priority: Major
>
> The [docs|https://impala.apache.org/docs/build3x/html/topics/impala_show.html] for {{SHOW FUNCTIONS}} says that we can use the following to list all built-in functions:
> {code:sql}
> show functions in _impala_builtins like '*week*';
> {code}
> However several Impala functions are removed early in the FE planning process and thus do not appear in the FE's function table in {{ScalarBuiltins}}: {{nvl2()}}, {{decode()}}, and {{nullif()}}. For example:
> {noformat}
> show functions in _impala_builtins like '*decode**'
> +-------------+------------------------------+-------------+---------------+
> | return type | signature                    | binary type | is persistent |
> +-------------+------------------------------+-------------+---------------+
> | STRING      | base64decode(STRING)         | BUILTIN     | true          |
> | STRING      | madlib_decode_vector(STRING) | BUILTIN     | true          |
> +-------------+------------------------------+-------------+---------------+
> {noformat}
> However, since these three are perfectly valid functions, would have expected them to appear in the table. How they are processed internally is an implementation detail unimportant to the end user.



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