Subject Re: [firebird-support] Table and Sequence names by reference
Author W O
Post date 2013-11-09T09:17:46Z
Sean, there are many times when to have a context variable with the name of the table would be good. For example when you have a stored procedure that is called from a trigger.

Trigger1 (table PRODUCTS)
-----------------------------------------
   EXECUTE PROCEDURE MyStoredProcedure('PRODUCTS');

Trigger2 (table CLIENTS)
--------------------------------------
   EXECUTE PROCEDURE MyStoredProcedure('CLIENTS');

Trigger3 (table COUNTRIES)
-----------------------------------------
   EXECUTE PROCEDURE MyStoredProcedure('COUNTRIES');


The problem with it is that if you write wrong the name of the table then you will have wrong results (i.e.: writing 'PRODUCTS' but the table is 'CLIENTS'). Therefore it would be very better having something like it:

   EXECUTE PROCEDURE MyStoredProcedure(TABLENAME);

where TABLENAME is a context variable that has the name of the table at which the trigger belongs. Never you will have wrong writings so.

If the stored procedure MyStoredProcedure is called from one or two tables then it is easy and fast to verify their correctness but if there are many tables with many triggers is another story.

Greetings.

Walter.






On Sat, Nov 9, 2013 at 12:29 AM, Leyne, Sean <Sean@...> wrote:
 

Walter,

 

A trigger can only apply to a single table, so why would you need a variable which would contain the table name?

 

You already have the explicit context -- you define the trigger.  So, if you want a variable, declare it and assign the value you want…

 

 

Sean

 

From: firebird-support@yahoogroups.com [mailto:firebird-support@yahoogroups.com] On Behalf Of W O
Sent: Friday, November 08, 2013 9:00 PM
To: firebird-support@yahoogroups.com
Subject: Re: [firebird-support] Table and Sequence names by reference

 




Really it would be nice to have the table's name when you are inside a trigger.

 

Greetings.

 

Walter.

 

 

On Fri, Nov 8, 2013 at 9:18 PM, Daniel L. Miller <dmiller@...> wrote:

 

On 11/7/2013 3:45 PM, Ann Harrison wrote:

On Thu, Nov 7, 2013 at 2:09 PM, Daniel L. Miller <dmiller@...> wrote:

Is it possible to refer to internal structures by reference in PSQL?

 

Err, reference, usually yes.  Change?  Probably not.  Basically, PSQL is

limited to DML - not DDL.

 

Ok - can you please clarify what I CAN do?  In particular:

1.  From within an insert/update trigger, is there a variable that provides the table name?  Or, if I'm trying to use a common stored procedure, would I call it from the trigger using the table name as a literal string parameter?

2.  Even if the DDL statement I used was wrong (and I admit that - I pasted it without going through it first) can you show me a valid DML?  Something like "SELECT * FROM :tablename"?

3.  My overly paranoid belt-and-suspenders isn't going to remain in production code (I hope).  I had that both as a safeguard and as an example to another programmer I'm working with.  The production code would just have the "standard" check to see if an id was passed, and otherwise perform the assignment of "new.id = NEXT VALUE FOR sequence".  But I'd like to have that code structure in a stored procedure so my triggers are basically just one line.  Is that wrong?

-- 
Daniel