Add an ifnull function to database connection classes

[Ryan J Ollos]

Copied from 12841#comment:2:

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One proposed change in [9f25cdfb3/rjollos.git].

When the group heading is NULL, it would be nice if Milestone (empty) was shown rather than just (empty). We could add an isnull function for each connection class and modify the reports. For example, on SQLite for report {3} we'd have:

-   'Milestone '||milestone AS __group__,
+   'Milestone '||ifnull(milestone,'(empty)') AS __group__,

I don't think it would be worth fixing up existing reports through a database upgrade step, but we could modify the reports in the database to affect new installations and add a note to TracUpgrade about how to manually modify reports.

[Jun Omae]

COALESCE() is portable.

[Ryan J Ollos]

Replying to Jun Omae:

Replying to Ryan J Ollos:

For example, on SQLite for report {3} we'd have:

-   'Milestone '||milestone AS __group__,
+   'Milestone '||ifnull(milestone,'(empty)') AS __group__,

If '(empty)' is embedded in the report, (empty) cannot be translated.

Will need to address this somehow in implementation.

[Ryan J Ollos]

Milestone renamed