I found this in the Postgres documentation, but it reads like jibberish to
me for the most part.
GROUP BY Clause
The optional GROUP BY clause has the general form
GROUP BY expression [, ...]
GROUP BY will condense into a single row all selected rows that share the
same values for the grouped expressions. expression can be an input column
name, or the name or ordinal number of an output column (SELECT list item),
or an arbitrary expression formed from input-column values. In case of
ambiguity, a GROUP BY name will be interpreted as an input-column name
rather than an output column name.
Aggregate functions, if any are used, are computed across all rows making
up each group, producing a separate value for each group (whereas without GROUP
BY, an aggregate produces a single value computed across all the selected
rows). When GROUP BY is present, it is not valid for the SELECT list
expressions to refer to ungrouped columns except within aggregate
functions, since there would be more than one possible value to return for
an ungrouped column.
On Sat, Feb 21, 2015 at 4:13 PM, TTambe <tambe...@gmail.com> wrote:
> Ok, so I need some help again. Every thing works great locally, but when I
> push to Heroku the controller code doesn't play nice with the Postgres
> database. Here is the controller again:
>
> @pin_albums = Pin.group(:album).order('artist asc')
>
> The error in my log is:
>
> ActionView::Template::Error (PG::GroupingError: ERROR: column "pins.id"
> must appear in the GROUP BY clause or be used in an aggregate function
>
> 2015-02-21T20:42:53.231456+00:00 app[web.1]: LINE 1: SELECT "pins".* FROM
> "pins" GROUP BY album ORDER BY artist...
>
> 2015-02-21T20:42:53.231458+00:00 app[web.1]: ^
>
> 2015-02-21T20:42:53.231460+00:00 app[web.1]: : SELECT "pins".* FROM
> "pins" GROUP BY album ORDER BY artist asc):
>
> 2015-02-21T20:42:53.231462+00:00 app[web.1]: 12: <th></th>
>
> 2015-02-21T20:42:53.231464+00:00 app[web.1]: 13:
> <th>Album</th>
>
> 2015-02-21T20:42:53.231466+00:00 app[web.1]: 14: </tr>
>
> 2015-02-21T20:42:53.231469+00:00 app[web.1]: 15: <%
> @pin_albums.each do |pin| %>
>
> 2015-02-21T20:42:53.231471+00:00 app[web.1]: 16: <tr>
>
> 2015-02-21T20:42:53.231473+00:00 app[web.1]: 17: <td><%=
> (last_artist == pin.artist) ? '' : pin.artist %></td>
>
> 2015-02-21T20:42:53.231475+00:00 app[web.1]: 18: <td><%=
> link_to image_tag(pin.image), pin %></td>
>
> 2015-02-21T20:42:53.231478+00:00 app[web.1]:
> app/views/pages/artists.html.erb:15:in
> `_app_views_pages_artists_html_erb__4200071474432892294_70083862737420'
>
>
> I've been Googling it, but any answers I've found haven't been clear
> enough for me to fix the issue. I see it says that pins.id must appear in
> the Group By clause, but I'm not clear on that.
>
>
> On Fri, Feb 20, 2015 at 1:22 PM, TTambe <tambe...@gmail.com> wrote:
>
>> You're absolutely right Colin, thanks. I'm not that familiar with that
>> simplified syntax of if/else statements, so I learned quite a bit from this
>> exchange!
>>
>> On Fri, Feb 20, 2015 at 3:57 AM, Colin Law <clan...@gmail.com> wrote:
>>
>>> On 20 February 2015 at 00:01, TTambe <tambe...@gmail.com> wrote:
>>> > I actually ended up doing this which worked:
>>> >
>>> > <% last_artist ||= nil %>
>>> >
>>> > <table id="artist">
>>> > <tr>
>>> > <th>Artist</th>
>>> > <th></th>
>>> > <th>Album</th>
>>> > </tr>
>>> > <% @pin_albums.each do |pin| %>
>>> > <% if last_artist != pin.artist %>
>>> > <tr>
>>> > <td><%= pin.artist %></td>
>>> > <td><%= link_to image_tag(pin.image), pin %></td>
>>> > <td><%= link_to pin.album, copy_pin_path(pin) %></td>
>>> > </tr>
>>> > <% else %>
>>> > <tr>
>>> > <td></td>
>>> > <td><%= link_to image_tag(pin.image), pin %></td>
>>> > <td><%= link_to pin.album, copy_pin_path(pin) %></td>
>>> > </tr>
>>> > <% end %>
>>> > <% last_artist = pin.artist %>
>>> > <% end %>
>>>
>>> You are right in that the key was to initialise last_artist at an
>>> appropriate scope.
>>> There are an awful lot of repeated lines there, Suppose you wanted to
>>> change the detail of the contents of the last cell in each row, you
>>> would have to change it in two places. You should put the if
>>> statement round just the first cell not round the whole row. so for
>>> that cell use something like
>>> <td>
>>> <%= (last_artist == pin.artist) ? '' : pin.artist %>
>>> </td>
>>> Or use an if statement inside the <td> </td> if you prefer. That is
>>> two single quotes in the line above of course.
>>>
>>> Colin
>>>
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>>
>>
>
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