Re: Join query help

Many many thanks for all the advice =)


On 21/08/07, Michael Glaesemann <grzm@seespotcode.net> wrote:
>
> On Aug 20, 2007, at 19:52 , novice wrote:
>
> > Try 2: Here are my DDLs & DMLs
>
> Thanks for the data. It looks like the data you provided in the first
> set was a little different, and the queries I supplied in my previous
> message give you the results you want.
>
> > CREATE TABLE record
> > (
> >   record_id integer PRIMARY KEY,
> >   record_date timestamp with time zone NOT NULL
> > );
> >
> > INSERT INTO record(record_id, record_date) VALUES ('1', '2007-07-23
> > 11:30:37');
>
> Note: record_id is in integer, yet you're quoting the value ('1').
> This causes the server to cast the text value to an integer. Here
> it's not going to cause much of a problem, just a couple CPU cycles.
> In table definitions (and possibly queries?) it can cause the server
> to ignore otherwise usable indexes when planning queries. (I see
> below your other inserts also quote integer values: you should drop
> the quotes there as well.)
>
> > CREATE TABLE score
> > (
> >   score_id integer PRIMARY KEY,
> >   score_description character(7) NOT NULL
> >
> > );
>
> Unless you have a strict business rule that score_description can
> have no more than 7 characters, you should just use text instead of
> character(7). It provides you more freedom (for example, you don't
> have to change the column type if you ever want to use longer
> descriptions). character(7) does not gain you anything in terms of
> performance.
>
> I'd also recommend adding a UNIQUE constraint to score_description.
> It appears your score_id has no meaning other than use as a surrogate
> key. There's nothing to prevent INSERT INTO score (score_id,
> score_description) VALUES (5, 'SAFE') which would be quite confusing,
> I should think. And if you don't have any particular reason to use a
> surrogate key, you could just use score_description as the primary
> key  of the table, dropping score_id altogether. it would reduce the
> number of joins you needed to do to have easily interpretable query
> results. (This all goes for your record table as well.)
>
> > I like to query for a result set that will also have the sum(score_id)
> > where score_id = '1' like the following
> >
> >    week   | records | inspections | score
> > ----------+---------+-------------+------
> >  2007, 30 |       2 |           8 |    6
> >  2007, 29 |       1 |           2 |    1
> > (2 rows)
> >
>
> (repeating from earlier post)
>
> SELECT to_char(record_week, 'YYYY, IW') as formatted_record_week
>      , count(DISTINCT record_id) AS record_count
>      , count(DISTINCT observation_id) AS observation_count
>      , safe_score_sum
> FROM record_with_week
> NATURAL JOIN observation
> NATURAL JOIN (
>      SELECT record_week, sum(score_id) as safe_score_sum
>      FROM record_with_week
>      NATURAL JOIN observation
>      NATURAL JOIN score
>      WHERE score_description = 'SAFE'
>      GROUP BY record_week
>      ) safe_observation
> GROUP BY record_week, safe_score_sum;
> formatted_record_week | record_count | observation_count |
> safe_score_sum
> -----------------------+--------------+-------------------
> +----------------
> 2007, 29              |            1 |                 2
> |              1
> 2007, 30              |            2 |                 8
> |              6
> (2 rows)
>
>
> > This will help identify that there were 6 SAFE observations found from
> > the 8 inspections on week 30.
>
> Yeah, I thought so: you're actually looking for the *count* of SAFE
> observations, not the sum of the score_id for 'SAFE'. So what you
> really want is:
>
> SELECT TO_CHAR(record_week, 'YYYY, IW') AS formatted_record_week
>      , count(DISTINCT record_id) AS record_count
>      , count(DISTINCT observation_id) AS observation_count
>      , count(DISTINCT safe_observation_id) as safe_observation_count
> FROM record_with_week
> NATURAL JOIN observation
> NATURAL JOIN (
>      SELECT record_week
>          , observation_id as safe_observation_id
>      FROM record_with_week
>      NATURAL JOIN observation
>      NATURAL JOIN score
>      WHERE score_description = 'SAFE'
>      ) safe_observation
> GROUP BY record_week;
> formatted_record_week | record_count | observation_count |
> safe_observation_count
> -----------------------+--------------+-------------------
> +------------------------
> 2007, 29              |            1 |                 2
> |                      1
> 2007, 30              |            2 |                 8
> |                      6
> (2 rows)
>
> Michael Glaesemann
> grzm seespotcode net
>
>
>
>