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From "Suran Jayathilaka (JIRA)" <j...@apache.org>
Subject [jira] Commented: (DERBY-712) Support for sequences
Date Sun, 26 Jul 2009 18:51:14 GMT

    [ https://issues.apache.org/jira/browse/DERBY-712?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=12735411#action_12735411

Suran Jayathilaka commented on DERBY-712:

Posting some question I had and the answers given by Rick. 

    * Like CreateTriggerNode etc, why isn't there a CreateFunctionNode? the functionDefinition()
method is using the CreateAliasNode class.
Good point. CREATE FUNCTION is a good template from the perspective of the parser but maybe
a bit confusing from the perspective of the data structures. Derby SQL routines (functions
and procedures) are called Aliases internally. This is because functions and procedures used
to be much lighter-weight objects. Originally, Derby functions and procedures were just names
(aliases) for user-coded static java methods, and declaring them was just a simple matter
of binding a Derby name to the external code. This, however, is not the ANSI syntax for declaring
functions and procedures. Today, Derby uses the ANSI language for declaring functions and
procedures, which means that functions and procedures are much more heavy-weight than the
original aliases were.

    * How are the various jj_2_*() mthods in SQLParser used?
    * In SQLParser, What's the sue of the jj_la1_* arrays?
Ah, looks like you are poking around in SQLParser. Don't bother with that file. The grammar
lives in sqlgrammar.jj, a yacc-like grammar which is much easier to understand and extend.
We use the javacc grammar generator to turn the sqlgrammar.jj source into a number of generated
files, one of which is the barely readable SQLParser which you're looking at right now. Let
me know if you need help understanding sqlgrammar.jj. It's fairly straightforward if you are
familiar with yacc-style grammars but you may need some pointers if you haven't worked on
one of these grammars before.

> Support for sequences
> ---------------------
>                 Key: DERBY-712
>                 URL: https://issues.apache.org/jira/browse/DERBY-712
>             Project: Derby
>          Issue Type: Improvement
>          Components: SQL
>         Environment: feature request 
>            Reporter: Tony Dahbura
>            Assignee: Suran Jayathilaka
>             Fix For:
>         Attachments: altertable.diff, catalogs_a.patch, catalogs_b.patch, catalogs_c.patch,
catalogs_d.patch, catalogs_e.patch, catalogs_f.patch, catalogs_f_2.patch, catalogs_g.diff,
catalogs_h.diff, SequenceGenerator.html
> Would like to see support added for sequences.  This would permit a select against the
sequence to always obtain a ever increasing/decreasing value.  The identity column works fine
but there are times for applications where the application needs to obtain the sequence number
and use it prior to the database write.  Subsequent calls to the table/column would result
in a new number on each call.
> SQL such as the following:
> SELECT NEXT VALUE FOR sequence_name FROM sometable ; would result in a next value.

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