[web-devel] Fwd: Sql join feature in persistent

[Paolo Losi]

2011/2/22 Антон Чешков <acheshkov at gmail.com>

> I want join  its by some rule and take only first "N" results. In this case
> i do not want serve all datasets entirely. I would like to make as little
> as possible.
> I think this algorithms  are exist.
>

Those algorithms exist indeed and have been implemented in last 25 years
inside RDBMS as query optimizers.
The question is, how much is that reasonable to re-implement in
Haskell/Persistent?
My 2 cent guess is that there are two viable options:

1) For Relational Backends, when scalability concerns raised by Max are not
important,
    the approach of a monadic DSL a la HaskellDB is the best.
    Basically the library job is to build the SQL query and let the RDBMS
optmizer
    do its job.

2) For NOSQL Backends, the solution is to code your hand rolled queries as
it can be
    done with persistent now (the "do nothing" solution). That is the
approach suggested
    for redis, for example...

Paolo




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Paolo Losi
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