[jira] [Commented] (CONNECTORS-110) Max activity and Max bandwidth reports don't work properly under Derby or HSQLDB

["Karl Wright (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/CONNECTORS-110?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13042669#comment-13042669 ] 

Karl Wright commented on CONNECTORS-110:
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Updated suggestion from Fred pertaining to HSQLDB:  Use WITH statement, as follows:

WITH invoice ( customerid, id, total) AS ( complex select statetment)
SELECT * FROM (SELECT DISTINCT customerid FROM invoice)  AS  i_one,
LATERAL ( SELECT id, total FROM invoice WHERE customerid =
i_one.customerid ORDER BY total DESC LIMIT 1) AS i_two

I believe this can actually be generated in a manner that fits the current abstraction.

> Max activity and Max bandwidth reports don't work properly under Derby or HSQLDB
> --------------------------------------------------------------------------------
>
>                 Key: CONNECTORS-110
>                 URL: https://issues.apache.org/jira/browse/CONNECTORS-110
>             Project: ManifoldCF
>          Issue Type: Bug
>          Components: Framework crawler agent
>            Reporter: Karl Wright
>
> The reason for the failure is because the queries used are doing the Postgresql DISTINCT ON (xxx) syntax, which Derby does not support.  Unfortunately, there does not seem to be a way in Derby at present to do anything similar to DISTINCT ON (xxx), and the queries really can't be done without that.
> One option is to introduce a getCapabilities() method into the database implementation, which would allow ACF to query the database capabilities before even presenting the report in the navigation menu in the UI.  Another alternative is to do a sizable chunk of resultset processing within ACF, which would require not only the DISTINCT ON() implementation, but also the enclosing sort and limit stuff.  It's the latter that would be most challenging, because of the difficulties with i18n etc.

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