Re: SQL flagger - Mailing list pgsql-hackers

THe SQL Flagger is only required for Intermediate SQL.  SQL'92 23.4 says Entry 
SQL may, but are not required to.

This said, it is a nice to have feature for the reasons that Peter pointed out.

But as I understand it, this is a sort of warning feature, and depending on the 
"extent of checking" option may be just something that the parser itself detects 
(Sysntax only) or something we detect in the analyzer code (catalog lookup). 
The second one has security issues (the standard suggests using a specific 
Information Schema) so we may want to avoid it for now.

Basically we would issue a FLAGGER message, if "level of flagging" is set to 
"Entry SQL Flagging" every time the parser finds a clause that is not Entry SQL.  Similarly for non Intermediate SQL
constructsif level is "Intermediate SQL 
 
Flagging". We would, of course, issue a FLAGGER message for all our PostgreSQL 
specific extensions in any level (if Flagging enabled).

If I understood it correctly, we only need a new elog level and add a few elog 
calls in some of gram.y clauses...

Regards,
Fernando

Tom Lane wrote:> Peter Eisentraut <peter_e@gmx.net> writes:
> 
>>The SQL standard requires conforming implementations to provide an
>>"SQL flagger" facility ...
> 
> 
>>I think we could implement this with relatively little intrusion if we
>>create an interface routine, say SQLFlagger(), which takes the entire
>>parsetree as its argument can then analyze the syntax in as much
>>detail as it likes.  (Of course that function would only be called if
>>a certain Boolean flag is set.)  But a few syntax elements would need
>>to checked right within gram.y, such as the omission of the drop
>>behavior or the use of TEMP vs. TEMPORARY, which is resolved right in
>>the parser and cannot be detected later.
> 
> 
>>Should we implement this?
> 
> 
> I think we would be better off to implement this as a standalone program
> rather than as a backend mode option.
> 
> In general, gram.y's behavior should never depend on any runtime
> variables.  If it does, you get inconsistent results from
>     SET var = val ; ... other stuff ...
> (one query string) compared to
>     SET var = val
>     ... other stuff ...
> (two query strings), because the whole query string is fed through
> gram.y before any of it is executed.
> 
> Plan B, if you really want to do this in the backend, would be to alter
> gram.y's output trees so that all the non-spec constructs are still
> recognizable in the raw parse tree, and any conversions needed are done
> in analyze.c's processing (which would also be the place to issue the
> flagger warnings).  This is not necessarily a bad idea; I've always
> thought that we do too much work in gram.y anyway.  But you will be
> fighting a permanent rear-guard action to keep people from
> re-introducing variant syntaxes by quick gram.y hacks.
> 
> In general I like the idea of a standalone program better, however.
> It would be able to have its own grammar tuned to its needs.  I don't
> think there would be much maintenance problem introduced thereby,
> since presumably the flagger's grammar is driven by the spec and won't
> need to change when we change what Postgres accepts.
> 
>             regards, tom lane
> 
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-- 
Fernando Nasser
Red Hat - Toronto                       E-Mail:  fnasser@redhat.com
2323 Yonge Street, Suite #300
Toronto, Ontario   M4P 2C9