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@spadim.com.br> 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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