Move DISTINCT to a query option

Here is a patch.

It convertes the distinct option, if set. I tested the patch quite intensive.

What about groupby? I don't know any contrib/custom backend which supports the option at the moment.

Applies, seems to work (did a quick test).

I agree that groupby should be handled the same (move it to query options), it's an sql thing, so it makes sense.
Doesn't need to happen in this issue though.

The patch applies to 7.x-3.x with fuzz; I re-rolled it and am attaching a version that applies cleanly. It moves the setting, but using 'distinct' still yields an error, since evidently new work is needed to support distinct queries on D7:

Exception: d7cx: Column-level distinct is not supported yet. in views_plugin_query_default->compile_fields() (line 940 of /shared/vash/sandboxes/white/barnard/site/www/sites/all/modules/views/plugins/views_plugin_query_default.inc).

See #863478: Distinct is not supported by dbtng

It still seems not to be supported? I'm confused a bit, and asked berdir.

Commited the patch with a commented out distinct option. Let's fix this later.

I'm not sure, but I think the commented out distinct option is why I'm getting undefined index errors on every View for this bit o' code:

    // Make the query distinct if the option was set.
    if ($this->options['distinct']) {
      // $this->set_distinct();
    }

Perhaps the if statement should have been commented out, too?

(Sorry, I don't know enough about how Views uses issue tags to tell if the alpha-4 blocker status is for 2.x or 3.x issues, so I'm leaving it alone for now.)

I think here should be used !empty

Alrighty, added an empty().

Thanks.

Follow-up issue: #1234048: Distinct requires workaround with bad usability to make 6.x-3.x-dev work like Views 2