MySQL joined select

Marek Reichenbach reichenbach.marek at gmail.com
Tue Mar 20 11:57:01 CDT 2012


Thanks for the replie!!! :), I'll make some research.

On 20 March 2012 18:38, Pete <pete at mollysrevenge.com> wrote:

> Hi Ken,
> Good catch on the multiple FROM clauses, not sure what that's all about.
>  Probably just needs to qualify the columns in the condition with the table
> name.
>
> The SELECT statement has a lot of problems in general.  There's no JOIN
> statement to link table1 and table2 together, for example.  That might work
> as long as the column(s) to be used to join the tables together have the
> same name in both tables but in general, it's much better to explicitly
> define the linkage with a JOIN statement - for clarity reasons if no other.
>
> Just one comment on the need to qualify columns with table names.  I
> definitely agree it's good practice to do that for clarity but as long as a
> column name is unique among all tables, SQL will figure out which table an
> unqualified column name belongs to.
>
> Pete
>
> On Tue, Mar 20, 2012 at 8:46 AM, Ken Ray <kray at sonsothunder.com> wrote:
>
> >
> > On Mar 20, 2012, at 4:20 AM, Marek Reichenbach wrote:
> >
> > > Thanks for the replies.
> > > I've made it workin, but I wanna add something else:
> > >
> > > So the question in SQL is:
> > >
> > > Maybe there is a way to hide columns it the result, like:
> > > SELECT car_nr, model, travel_days FROM table1,table2 WHERE number <>
> 414
> > > AND (car_nr > truck_nr) from transport;
> > > and show only result of the colums travel_days, but ONLY on*
> > > **separate* columns
> > > and  HIDE OTHER COLUMNS.
> >
> > You only include the columns you want back in the SELECT part of the
> query:
> >
> > SELECT travel_days FROM …
> >
> > Also, although I know you provided a dummy query, be aware that there are
> > two inherent problems with the one you provided:
> >
> > 1) If you have multiple tables in the FROM clause, you need to identify
> > the table attached to the column in the SELECT clause (although some SQL
> > engines might just assume you meant the first table, it's good form to
> > identify the table), either by full name:
> >
> >  SELECT table1.travel_days FROM table1,table2 WHERE…
> >
> > or by alias:
> >
> >  SELECT t1.travel_days FROM table1 t1,table2 t2 WHERE…
> >
> > 2) I'm not sure what "from transport" means since you already have a FROM
> > clause in your example query
> >
> > The bottom line is that you don't have to include columns in the SELECT
> > portion of the query that you don't want back, so long as you identify
> them
> > properly and they actually exist in the table you're referencing.
> >
> > Just be aware that LiveCode's text parsing is second to none, so there
> are
> > usually times where it may actually be easier and more efficient to let
> SQL
> > handle getting the data, but let LiveCode handle parsing the data after
> it
> > arrives. As I mentioned in an earlier post, you *can* use SQL to change
> > your numbers to "+" symbols, but it's ugly - Mark's method to
> post-process
> > it in LC with a single statement if far better (IMHO).
> >
> > Ken Ray
> > Sons of Thunder Software, Inc.
> > Email: kray at sonsothunder.com
> > Web Site: http://www.sonsothunder.com/
> >
> > _______________________________________________
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> >
>
>
> --
> Pete
> Molly's Revenge <http://www.mollysrevenge.com>
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