maria-discuss team mailing list archive

[Pantelis Theodosiou <ypercube@xxxxxxxxx>]

Did you mean to write

ORDER BY value ASC   and   ORDER BY value DESC

in the subqueries? The "ORDER BY date" doesn't make sense in the subqueries
as all the rows will have the same date, due to the "WHERE date=a.date"
correlation.

Pantelis


On Sat, Oct 3, 2015 at 2:12 AM, Roberto Spadim <roberto@xxxxxxxxxxxxx>
wrote:

> Hi guys
> I have a problem and a possible solution, that i think is relative easy to
> develop (i didn't tested but i think the source is easy to change)
>
> i have some queries like:
>
>
> SELECT
> date,
> (SELECT value FROM some_table WHERE date=a.date ORDER BY date ASC LIMIT 1)
> AS first,
> (SELECT value FROM some_table WHERE date=a.date ORDER BY date DESC LIMIT
> 1) AS last
> FROM some_table AS a
> GROUP BY date
>
>
> i want to "convert" the complex sub query, to a agregate function, and i
> thinking about group concat:
> from mysql docs:
>
> GROUP_CONCAT([DISTINCT] *expr* [,*expr* ...]
>              [ORDER BY {*unsigned_integer* | *col_name* | *expr*}
>                  [ASC | DESC] [,*col_name* ...]]
>              [SEPARATOR *str_val*])
>
>
> we have ORDER BY
> if we could include a "LIMIT" clause, i could rewrite this query to:
>
> SELECT
> date,
> GROUP_CONCAT(value ORDER BY date ASC LIMIT 1) AS first,
> GROUP_CONCAT(value ORDER BY date DESC LIMIT 1) AS last
> FROM some_table AS a
> GROUP BY date
>
>
> i know that i could have stats tables / materialized views (with flexview,
> i already tested :) ), but i want something more "easy to use" and not
> "very fast", just a "feature" to solve small problems
>
>
> it's a nice idea? does anyone have this "problem" and solve with other
> solutions?
>
> --
> Roberto Spadim
>
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