I am trying to get a top-down understanding of what an RDBMS does to
go
from a SQL Query to actual data (records served up).

Your thoughts / Links to good resources that cover this would be much
appreciated.


-David

David wrote:

Look for some books co-authored by Hector Garcia-Molina, Jeffrey D.
Ullman, and Jennifer Widom.

On Sat, 12 Sep 2009 09:03:03 -0700 (PDT), David wrote:

Hi David,

I guess that there will be differences between vendors. For Microsoft
SQL Server, the high level path is:

* Parse (includes syntax checking and transforming to an internal
structure, called parse tree IIRC)

* Optimize (based on statistical information on data distribution,
indexes present, trusted constraints, et al, choose one of the many ways
in which the query can be satisfied - basically transforming the parse
tree to an execution plan)

* Execute (based on execution plan, access data, combine, filter,
evaluate etc until desired results are attained).

Each of these steps is probably complex enough to warrant whole books,
though obviously much of the finer details would be privvy to MS staff
only.

Also, I left out some optimization steps such as using a hash of the
query to check if there is an execution plan for it already in the
procedure cache, parametrizing it so that identical queries in which
only hard-coded constants change can re-use the same execution plan,
etc.

Best, Hugo