SQL99 Hierarchical queries

I have done initial implementation of SQL99 WITH clause (attached).
It's now only for v7.3.4 and haven't a lot of checks and restrictions.

What kind of restrictions are on it?

Chris

I have done initial implementation of SQL99 WITH clause (attached).
It's now only for v7.3.4 and haven't a lot of checks and restrictions.

What kind of restrictions are on it?

Main restriction is that the query inside WITH alias can refer only to
back and to itself.
For example
WITH a as (...),b as (...)select ...;
a can refer only to itself, b - to a and b.

Its needed to restrict WITH aliased query not to use WITH aliasing
itself, i.e. avoid situation of WITH inside WITH. And make also some
other checks. But this isn't done yet.

Regards, Evgen.

hello,

I tested you patch, and it's good work. I would all methods in PostgreSQL.
I found query which kill backand

WITH t AS (
SELECT 0::int AS i
UNION ALL SELECT i + 1 FROM t WHERE i < 100)
SELECT * FROM t;

Regards
Pavel Stehule

Ok, I'm started porting it to 8.0.1 and will fix this also.
By the way, did you know any test suit for such queries? To make some
regression test.

Regards, Evgen

On Mon, Feb 28, 2005 at 11:07:51AM +0300, Evgen Potemkin wrote:

Ok, I'm started porting it to 8.0.1 and will fix this also. By the
way, did you know any test suit for such queries? To make some
regression test.

Evgen,

Thanks very much for doing this work. Is there some way you can
summarize what you did so others can join you in working on it? If it
is easier for you to write this in some language other than English,
please do, and we'll find translators :)

I noticed that the patch touches the parser, the optimizer and the
executor. What does it to with each? What did I miss?

Cheers,
D
--
David Fetter david@fetter.org http://fetter.org/
phone: +1 510 893 6100 mobile: +1 415 235 3778

Remember to vote!

I'm curious what kind of performance differences there would be over
using something like the nested-set model?

Would this be faster, or slower?

On Thu, 2005-02-24 at 13:02 +0300, Evgen Potemkin wrote:

Hi hackers!

I have done initial implementation of SQL99 WITH clause (attached).
It's now only for v7.3.4 and haven't a lot of checks and restrictions.
It can execute only simple WITH queries like
WITH tree AS (SELECT id,pnt,name,1::int AS level FROM t WHERE id=0
UNION SELECT t.id,t.pnt,t.name,tree.level+1 FROM t JOIN tree ON
tree.id=t.pnt ) SELECT * FROM tree;
It would be great if someone with knowledge of Pg internals can make a
kind of code review and make some advices how to better implement all
this.

Regards, Evgen.
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Mike Benoit <ipso@snappymail.ca>

On Mon, 28 Feb 2005, Evgen Potemkin wrote:

Ok, I'm started porting it to 8.0.1 and will fix this also.
By the way, did you know any test suit for such queries? To make some
regression test.

Hello, I can find some examples on internet and prepare regression tests.
I think PostgreSQL can support all syntax H.Q. Is more easy created
question via Oracle syntax, and processing is faster (maybe better
optimalisation now), than ANSI WITH syntax. Can You add support for
clausule VALUE?

Pavel Stehule

Mike,

I'm curious what kind of performance differences there would be over
using something like the nested-set model?

Would this be faster, or slower?

The answer is "yes". ;-)

Which tree structures you use depends on what you're trying to accomplish and
what your use case is. There are some structures (for example, heirarchical
org charts) for which nested sets can't be beat. There are plenty of
reasons to implement other tree structures, such as graphs, cycles, and
delimited lists depending on what you're trying to depict.

What WITH is going to "replace", if anything, is the simple adjacency list
structure.

--
Josh Berkus
Aglio Database Solutions
San Francisco

Thanks very much for doing this work. Is there some way you can
summarize what you did so others can join you in working on it? If it
is easier for you to write this in some language other than English,
please do, and we'll find translators :)

I noticed that the patch touches the parser, the optimizer and the
executor. What does it to with each? What did I miss?

Cheers,
D

Ok, i'll make some doc on this topic.

Regards, Evgen

Ok, I'm started porting it to 8.0.1 and will fix this also.
By the way, did you know any test suit for such queries? To make some
regression test.

Hello, I can find some examples on internet and prepare regression tests.
I think PostgreSQL can support all syntax H.Q. Is more easy created
question via Oracle syntax, and processing is faster (maybe better
optimalisation now), than ANSI WITH syntax. Can You add support for
clausule VALUE?

Pavel Stehule

On this weekend I'll see to DB2 reference and if there some
description on what is it, I'll try to implement it.

Regards, Evgen.

Hello hackers,

Thanks very much for doing this work. Is there some way you can
summarize what you did so others can join you in working on it? If it
is easier for you to write this in some language other than English,
please do, and we'll find translators :)

I noticed that the patch touches the parser, the optimizer and the
executor. What does it to with each? What did I miss?

This is some info about implementations.

Parser.
WITH aliased queries stored as list of SUBQUERY nodes. Each of
them is parsed as usually. In pstate->withClause already analyzed part
of WITH queries list is stored. When next WITH subquery is analyzed,
it's been added to subqueries list inside withClause node, so any WITH
subquery can see al prevoius WITH subqueries.
In FROM clause all WITH aliases represented by special type of
RangTblEntry - RTE_WITH_SUBQUERY. It stores a reference to WithClause
node and index of itself in QITH subqueries list.
For analyzing var added step to search in WITH aliases if they are present.
Recursiveness support. Before WITH subquery analyzing in
pstate->withClause->calias stored it's alias. So when transforming
FROM clause item and relation name found only in
pstate->withClause->calias query marked as recursive. SQL99 recursive
queries are made using UNION and first UNION subquery should be non
recursive (this isn't currently checked). Thus when transforming set
operation statement, after analyzing of first statement it's is RTE
stored in pstate->withClause->cRTE, and all checks for vars in this
WITH subquery in made against this RTE.

Optimizer.
WithClause node transformed to With node, scan of RTEs of type
RTE_WITH_SUBQUERY to WithScan nodes. Each WITH subquery is enveloped
into WithSubPlan node. It stores result and working tuplestores, and
some flags (used for prevent double initialization and execution) for
each subquery.
Nothing extraordinary is done here.

Executor.
When executor tries to fetch first tuple from any WithScan node,
this node check whether With node have been executed, if no then it
executes it and then fetches all it's tuples from it's result
tuplestore.
"With" node being executed is simply call ExecNode on each subplan
in it's list and storing tuples in result tuplestore.
Recursiveness support. It's all done in Append node. If it marked
as recusrive, it changes a little it's behaviour.
Tuples fetched from subplan are stored in workin table. When
Append reaches the end of list of its subqueries it call
nodeWithSwitchTables. This function for query being executed will
append result table to final table, move working table to result
table, and clean working table. After this Append begins next loop of
subqueries execution, starting from 2nd subquery. Thus first Append
subquery is executed only once. Execution ends when no one tuple
fetched from all subqueries.
This approach allows WithScan nodes to fetch data fetched by
Append in previous loop.

Regards, Evgen.

Hi Evgen,

How's the syncing with HEAD going?

Cheers,

Chris

Evgen Potemkin wrote:

Hi Evgen,

How's the syncing with HEAD going?

Cheers,

Chris

I'm working on it.

Regards, Evgen.

Hi Evgen,

I just keep pinging this patch thread every once in a while to make sure
it doesn't get forgotten :)

How is the syncing with 8.1 CVS coming along?

Chris

Evgen Potemkin wrote: