Обсуждение: column name gets substitudes inside an execute statement of a trigger function. how to avoid it?!

Hello list.
I'm a newbie with plpgsql, so I'm sorry for doing stupid questions...
I have a situation whit one table where items are related to two other
tables through a common id (unique in the first table) and the table
name. Whenever the user execute an operation on an item of the first
one ("prima"), the related items in tables "seconda" or "terza" must
be updated.

CREATE TABLE prima
(
  id serial NOT NULL,
  nome character varying(100),
  table character varying(10), ## this contains "seconda" or "terza"
  CONSTRAINT prima_pkey PRIMARY KEY (id)
)

CREATE TABLE seconda
(
  id serial NOT NULL,
  nome character varying(100),
  CONSTRAINT seconda_pkey PRIMARY KEY (id)
)

CREATE TABLE seconda
(
  id serial NOT NULL,
  nome character varying(100),
  CONSTRAINT seconda_pkey PRIMARY KEY (id)
)


So I need to retrieve the table name dynamically inside the function,
and AFAIK I can do it only using an execute statement. BUT when I do
something like "INSERT INTO prima (nome,table) VALUES
('lets_try','seconda')"  I get the following error:

ERROR: Column 'lets_try' does not exist
LINE 1: INSERT INTO seconda (nome) VALUES ('lets_try')

My function and trigger are:

CREATE OR REPLACE FUNCTION fun1() RETURNS TRIGGER AS
$primaprova$
DECLARE
nome varchar;
BEGIN
IF (TG_OP='INSERT') THEN
execute 'INSERT INTO ' || NEW.table || ' (nome) VALUES( "' || NEW.nome
|| '" );';
RETURN NEW;
ELSEIF (TG_OP='UPDATE') THEN
execute 'UPDATE '|| NEW.table ||' SET nome='|| NEW.nome ||';';
RETURN NEW;
ELSEIF (TG_OP='DELETE') THEN
execute 'DELETE FROM '|| OLD.table ||' where nome='|| OLD.nome ||';';
RETURN OLD;
END IF;
END;
$primaprova$ LANGUAGE plpgsql;
CREATE TRIGGER tr1 AFTER INSERT OR UPDATE OR DELETE ON prima FOR EACH
ROW EXECUTE PROCEDURE fun1();

It seems like the string 'nome' inside the execute statement gets
substituded by the NEW.nome value, while it shouldn't.
How can I solve this? Where am I wrong?

Thanks a lot,
Gioanni

PS: I'm using PG 1.8.4 on Windows XP

G. Allegri wrote:
>
> ERROR: Column 'lets_try' does not exist
> LINE 1: INSERT INTO seconda (nome) VALUES ('lets_try')
>
> My function and trigger are:
>
> CREATE OR REPLACE FUNCTION fun1() RETURNS TRIGGER AS
> $primaprova$
> DECLARE
> nome varchar;
> BEGIN
> IF (TG_OP='INSERT') THEN
> execute 'INSERT INTO ' || NEW.table || ' (nome) VALUES( "' || NEW.nome
> || '" );';

This will give VALUES ("lets_try") which is not a valid way to quote a
string. It *is* a valid way to quote an identifier (e.g. a column).

You probably want to use the quote_literal() function anyway to escape
any single-quotes in the value being quoted.

--
   Richard Huxton
   Archonet Ltd

Great, quote_literal() solved it! It was so easy :)

Thx Richard

2009/6/9 Richard Huxton <dev@archonet.com>:
> G. Allegri wrote:
>>
>> ERROR: Column 'lets_try' does not exist
>> LINE 1: INSERT INTO seconda (nome) VALUES ('lets_try')
>>
>> My function and trigger are:
>>
>> CREATE OR REPLACE FUNCTION fun1() RETURNS TRIGGER AS
>> $primaprova$
>> DECLARE
>> nome varchar;
>> BEGIN
>> IF (TG_OP='INSERT') THEN
>> execute 'INSERT INTO ' || NEW.table || ' (nome) VALUES( "' || NEW.nome
>> || '" );';
>
> This will give VALUES ("lets_try") which is not a valid way to quote a
> string. It *is* a valid way to quote an identifier (e.g. a column).
>
> You probably want to use the quote_literal() function anyway to escape any
> single-quotes in the value being quoted.
>
> --
>  Richard Huxton
>  Archonet Ltd
>

Stephan, you're rigth. It was just a first try. In the real situation
"seconda" and "terza" have a prima_id column. So the right one is:

execute 'UPDATE '|| NEW.tabella ||' SET nome='||
quote_literal(NEW.nome) ||' WEHERE prima_id=' || NEW.id || ';';

I though that double apices would quote. That was the error.
quote_literal() solves it.

2009/6/9 Stephan Szabo <sszabo@megazone.bigpanda.com>:
> On Tue, 9 Jun 2009, G. Allegri wrote:
>
>> Hello list.
>> I'm a newbie with plpgsql, so I'm sorry for doing stupid questions...
>> I have a situation whit one table where items are related to two other
>> tables through a common id (unique in the first table) and the table
>> name. Whenever the user execute an operation on an item of the first
>> one ("prima"), the related items in tables "seconda" or "terza" must
>> be updated.
>>
>> CREATE TABLE prima
>> (
>>   id serial NOT NULL,
>>   nome character varying(100),
>>   table character varying(10), ## this contains "seconda" or "terza"
>>   CONSTRAINT prima_pkey PRIMARY KEY (id)
>> )
>>
>> CREATE TABLE seconda
>> (
>>   id serial NOT NULL,
>>   nome character varying(100),
>>   CONSTRAINT seconda_pkey PRIMARY KEY (id)
>> )
>>
>> CREATE TABLE seconda
>> (
>>   id serial NOT NULL,
>>   nome character varying(100),
>>   CONSTRAINT seconda_pkey PRIMARY KEY (id)
>> )
>>
>>
>> So I need to retrieve the table name dynamically inside the function,
>> and AFAIK I can do it only using an execute statement. BUT when I do
>> something like "INSERT INTO prima (nome,table) VALUES
>> ('lets_try','seconda')"  I get the following error:
>>
>> ERROR: Column 'lets_try' does not exist
>> LINE 1: INSERT INTO seconda (nome) VALUES ('lets_try')
>
> Are you sure that's the error message (specifically the context)?
> Specifically, the query below in the function looks like it would
> generate:
>
> INSERT INTO seconda (name) VALUES ("lets_try")
>
> which means use lets_try as a quoted column name, as opposed to
> ('lets_try') which means the string literal.
>
> In addition, what are the semantics of update supposed to be? It looks
> like if you update a row in prima, it's going to set all the name fields
> to the new name? Is that intentional, or was the intent to change only the
> row with the old name?
>
>> CREATE OR REPLACE FUNCTION fun1() RETURNS TRIGGER AS
>> $primaprova$
>> DECLARE
>> nome varchar;
>> BEGIN
>> IF (TG_OP='INSERT') THEN
>> execute 'INSERT INTO ' || NEW.table || ' (nome) VALUES( "' || NEW.nome
>> || '" );';
>> RETURN NEW;
>> ELSEIF (TG_OP='UPDATE') THEN
>> execute 'UPDATE '|| NEW.table ||' SET nome='|| NEW.nome ||';';
>> RETURN NEW;
>> ELSEIF (TG_OP='DELETE') THEN
>> execute 'DELETE FROM '|| OLD.table ||' where nome='|| OLD.nome ||';';
>> RETURN OLD;
>> END IF;
>> END;
>> $primaprova$ LANGUAGE plpgsql;
>> CREATE TRIGGER tr1 AFTER INSERT OR UPDATE OR DELETE ON prima FOR EACH
>> ROW EXECUTE PROCEDURE fun1();
>

On Tue, 9 Jun 2009, G. Allegri wrote:

> Hello list.
> I'm a newbie with plpgsql, so I'm sorry for doing stupid questions...
> I have a situation whit one table where items are related to two other
> tables through a common id (unique in the first table) and the table
> name. Whenever the user execute an operation on an item of the first
> one ("prima"), the related items in tables "seconda" or "terza" must
> be updated.
>
> CREATE TABLE prima
> (
>   id serial NOT NULL,
>   nome character varying(100),
>   table character varying(10), ## this contains "seconda" or "terza"
>   CONSTRAINT prima_pkey PRIMARY KEY (id)
> )
>
> CREATE TABLE seconda
> (
>   id serial NOT NULL,
>   nome character varying(100),
>   CONSTRAINT seconda_pkey PRIMARY KEY (id)
> )
>
> CREATE TABLE seconda
> (
>   id serial NOT NULL,
>   nome character varying(100),
>   CONSTRAINT seconda_pkey PRIMARY KEY (id)
> )
>
>
> So I need to retrieve the table name dynamically inside the function,
> and AFAIK I can do it only using an execute statement. BUT when I do
> something like "INSERT INTO prima (nome,table) VALUES
> ('lets_try','seconda')"  I get the following error:
>
> ERROR: Column 'lets_try' does not exist
> LINE 1: INSERT INTO seconda (nome) VALUES ('lets_try')

Are you sure that's the error message (specifically the context)?
Specifically, the query below in the function looks like it would
generate:

INSERT INTO seconda (name) VALUES ("lets_try")

which means use lets_try as a quoted column name, as opposed to
('lets_try') which means the string literal.

In addition, what are the semantics of update supposed to be? It looks
like if you update a row in prima, it's going to set all the name fields
to the new name? Is that intentional, or was the intent to change only the
row with the old name?

> CREATE OR REPLACE FUNCTION fun1() RETURNS TRIGGER AS
> $primaprova$
> DECLARE
> nome varchar;
> BEGIN
> IF (TG_OP='INSERT') THEN
> execute 'INSERT INTO ' || NEW.table || ' (nome) VALUES( "' || NEW.nome
> || '" );';
> RETURN NEW;
> ELSEIF (TG_OP='UPDATE') THEN
> execute 'UPDATE '|| NEW.table ||' SET nome='|| NEW.nome ||';';
> RETURN NEW;
> ELSEIF (TG_OP='DELETE') THEN
> execute 'DELETE FROM '|| OLD.table ||' where nome='|| OLD.nome ||';';
> RETURN OLD;
> END IF;
> END;
> $primaprova$ LANGUAGE plpgsql;
> CREATE TRIGGER tr1 AFTER INSERT OR UPDATE OR DELETE ON prima FOR EACH
> ROW EXECUTE PROCEDURE fun1();