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Thank you for the link Merlin. > Date: Thu, 10 Mar 2011 08:22:13 -0600 > Subject: Re: 9.1 Trigger question > From: mmoncure@xxxxxxxxx > To: michaelblack75052@xxxxxxxxxxx > CC: pgsql-general@xxxxxxxxxxxxxx > > On Wed, Mar 9, 2011 at 8:24 PM, Michael Black > <michaelblack75052@xxxxxxxxxxx> wrote: > > The following from 9.1 documentation on triggers ---- > > > > "SQL allows you to define aliases for the "old" and "new" rows or tables for > > use in the definition of the triggered action (e.g., CREATE TRIGGER ... ON > > tablename REFERENCING OLD ROW AS somename NEW ROW AS othername ...). Since > > PostgreSQL allows trigger procedures to be written in any number of > > user-defined languages, access to the data is handled in a language-specific > > way. " > > > > This seems to imply that triggers actually have to reference a function > > rather than containing the actual code for the trigger to perform. For > > example the only valid format of a trigger is to > > > > CREATE TRIGGER view_insert > > --- other parameters here --- > > EXECUTE PROCEDURE view_insert_row(); > > > > Instead of the normal way > > > > CREATE TRIGGER view_insert > > --- other parameters here --- > > AS > > --- sql functions, conditions and statements --- > > ; > > > > Is my understand in of this correct? If so, how does the other language > > know the old record from the new? > > This is correct. In PostgreSQL, the trigger function is always > separate from the trigger definition. Procedures written in various > languages in PostgreSQL have to wrap an internal API that provides > access to various features, querying, etc. Take a look for example > how it is exposeed in python: > http://www.postgresql.org/docs/9.0/interactive/plpython-trigger.html > -- if you wanted to see how that was done you could look at the code > for the python language handler. > > merlin |
