Re: [SQL] Rules and referential integrity

> Now: why not define a function (in pltcl; could be something else?)
>
>  create function err(bpchar) returns bpchar
>    as 'error $1' language 'pltcl'
>
> Then, if the value of a column does not appear in another table, you
> could rewrite the query to (for instance)
>       select err('your message')
>
> This will raise a PGRES_FATAL_ERROR , with error message
> ERROR:  pltcl: your message
>
> So: it is possible. Why it is better (or worse) than a trigger, I do
> not know. Views on that?

    Depends  on  the  data  and  usage.  If  only  few tuples are
    affected by a statement, a trigger will usually do  a  better
    job.  Especially  if  the  path  to  find  that tuple is very
    complicated, because the rule has to follow this path another
    time.

    OTOH  if one statement affects thousands of rows, a rule will
    perform better because it is executed in one  internal  extra
    query  instead of invoking the trigger for each single tuple.

    There is no general "this is better than that".


Jan

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