Re: [HACKERS] Re: [SQL] RULE questions.

Hi,

I have what I first thought would be a trivial problem, in that I require
the 2 VARCHAR columns in the following table to have the data stored in
upper case.

test_table
+-----------------------------+------------------------------+------+
| Field | Type |Length|
+-----------------------------+------------------------------+------+
| user_id | int4 | 4 |
| name | varchar() | 10 |
| password | varchar() | 10 |
+-----------------------------+------------------------------+------+

I considered just using UPPER() in every SELECT statement, or creating a
view that SELECTed the 2 VARCHAR cols using UPPER but I assume that this
would have more performance issues than having the data converted to
uppercase only once during an insert or update. (Please correct me if I am
wrong).

After looking at triggers and rules I came up with the following solution:

CREATE VIEW test AS SELECT * FROM test_table;

CREATE RULE insert_test AS
ON INSERT TO test DO INSTEAD
INSERT INTO test_table (user_id, name, password) VALUES(new.user_id,
UPPER(new.name), UPPER(new.password));

CREATE RULE update_test AS
ON UPDATE TO test DO INSTEAD
UPDATE test_table SET name = UPPER(new.name), password = UPPER(new.password)
WHERE user_id = new.user_id;

which means that any insert or update to the test view is stored in upper
case as required.

However, I still have two concerns about this.

1) What impact on performance does using a VIEW in this way have?
2) Users can still enter data straight into test_table in lower case
bypassing the "rules"

First off, is there an easier way to ensure that data is stored in uppercase
for certain columns (not the whole table). And if not does anyone have
comments on performance issues, or ways of stopping users accidentally or
intentionally inserting lower case data straight into the table rather than
the view?

Many thanks in advance,

---[ Neil Burrows ]-----------------------------------------------------
E-mail: neil(dot)burrows(at)gssec(dot)bt(dot)co(dot)uk British Telecom Plc.
: neil(at)pawprint(dot)co(dot)uk Glasgow Engineering Centre
Web : http://www.remo.demon.co.uk/ Highburgh Rd. Glasgow UK
-----------< Any views expressed are not those of my employer >-----------

>
> Hi,
>
> I have what I first thought would be a trivial problem, in that I require
> the 2 VARCHAR columns in the following table to have the data stored in
> upper case.
>
> test_table
> +-----------------------------+------------------------------+------+
> | Field | Type |Length|
> +-----------------------------+------------------------------+------+
> | user_id | int4 | 4 |
> | name | varchar() | 10 |
> | password | varchar() | 10 |
> +-----------------------------+------------------------------+------+
>
>
> I considered just using UPPER() in every SELECT statement, or creating a
> view that SELECTed the 2 VARCHAR cols using UPPER but I assume that this
> would have more performance issues than having the data converted to
> uppercase only once during an insert or update. (Please correct me if I am
> wrong).

It's right.

>
> After looking at triggers and rules I came up with the following solution:
>
> CREATE VIEW test AS SELECT * FROM test_table;
>
> CREATE RULE insert_test AS
> ON INSERT TO test DO INSTEAD
> INSERT INTO test_table (user_id, name, password) VALUES(new.user_id,
> UPPER(new.name), UPPER(new.password));
>
> CREATE RULE update_test AS
> ON UPDATE TO test DO INSTEAD
> UPDATE test_table SET name = UPPER(new.name), password = UPPER(new.password)
> WHERE user_id = new.user_id;

1. Make sure user_id is unique or extend the WHERE clause in
the UPDATE rule. To explain why:

user_id | name
--------+----------
1 | aaa
1 | bbb
2 | ccc

UPDATE test SET name = 'ddd' WHERE name = 'aaa';

user_id | name
--------+----------
1 | ddd
1 | ddd
2 | ccc

This is because the rule will find the user_id 1 for name
'aaa' and then updates any row with user_id 1.

2. Change the WHERE clause in the UPDATE rule to compare
against old.user_id and add "user_id = new.user_id" to
the SET clause. Otherwise it would not be possible to
change the user_id because this thrown away by the rule.

3. Don't forget the ON DELETE rule. Maybe you don't want
once given user_id's to be changed or deleted. Then 2.
and 3. aren't right.

>
> which means that any insert or update to the test view is stored in upper
> case as required.
>
> However, I still have two concerns about this.
>
> 1) What impact on performance does using a VIEW in this way have?

Only the rewriting overhead per query. The rewrite system
changes the querytree generated by the parser in such a way
that the planner/optimizer will get the same input as if the
query really was the SELECT from test_table. If you have a
view

CREATE VIEW test AS SELECT * FROM test_table;

the two statements

SELECT * FROM test;
SELECT * FROM test_table;

are totally equivalent from the planners/optimizers (and so
from the executors) point of view. The rewriting overhead
depends on how complex the statements and rule definitions
are. But not on the number of rows affected in the statement.
Selecting thousands of rows has the same speed than doing it
from the real tables behind a view. It's very small because
compared against parser/planner/optimizer it has to do very
few system cache lookups and works mostly with the data that
is already in memory.

> 2) Users can still enter data straight into test_table in lower case
> bypassing the "rules"

Not necessarily. Since v6.4 rule actions (in contrast to
triggers up to now) inherit the access permissions of the
owner of the relation they're fired on.

CREATE TABLE test_table ...;
CREATE VIEW test AS SELECT * FROM test_table;

REVOKE ALL ON test_table FROM public;
GRANT ALL ON test_table TO me;

REVOKE ALL ON test FROM public;
GRANT ALL ON test TO me;
GRANT SELECT, INSERT, UPDATE, DELETE ON test TO public;

Now any user can access test, but nobody but me can access
test_table. Not even a SELECT does work. They can do most
things on test. But the rule actions are executed under the
permissions of me, so they work silently.

YOU MUST NOT GRANT ALL TO PUBLIC. ALL includes RULE
permission, so a user could change the rules on test, do some
things (maybe on any of your other tables) and reinstall the
original state of rules!

In addition to that, consider the case you really don't want
once given user_id's ever to change. Nor you like them to be
ever reused. But they should disappear on DELETE.

CREATE TABLE test_table (user_id int,
name varchar(10),
pass varchar(10),
alive bool);

CREATE UNIQUE INDEX test_user_id ON test_table (user_id);

CREATE VIEW test AS SELECT * FROM test_data
WHERE alive;

CREATE RULE ins_test AS ON INSERT TO test
DO INSTEAD INSERT INTO test_table
VALUES (new.user_id, UPPER(new.name), UPPER(new.pass), 't');

CREATE RULE upd_test AS ON UPDATE TO test
DO INSTEAD UPDATE test_table
SET name = UPPER(new.name), pass = UPPER(new.pass)
WHERE user_id = old.user_id AND alive;

CREATE RULE del_test AS ON DELETE TO test
DO INSTEAD UPDATE test_table
SET alive = 'f'
WHERE user_id = old.user_id AND alive;

Plus all the REVOKE and GRANT. This setup denies changes to
user_id, makes the row's disappear on DELETE but throw's an
error 'cannot insert duplicate ...' if someone tries to reuse
a user_id. Only the owner of the test_table can reincarnate a
once deleted account.

>
> First off, is there an easier way to ensure that data is stored in uppercase
> for certain columns (not the whole table). And if not does anyone have
> comments on performance issues, or ways of stopping users accidentally or
> intentionally inserting lower case data straight into the table rather than
> the view?

The Postgres rewrite rule system is the most powerful way to
do that.

Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck(at)debis(dot)com (Jan Wieck) #

Thus spake Neil Burrows
> First off, is there an easier way to ensure that data is stored in uppercase
> for certain columns (not the whole table). And if not does anyone have
> comments on performance issues, or ways of stopping users accidentally or
> intentionally inserting lower case data straight into the table rather than
> the view?

This makes me think of two features missing in PostgreSQL that I would
love to see. I know it's probably to late to think about it now for
6.5 but I wonder what others think about this.

First, as suggested above, how about an option to automatically convert
data to upper case on entry? I realize that triggers can do the job but
it seems to be needed often enough that putting it into the definition
for the field seems useful. I guess a lower option would make sense too.

Second, an option to CREATE INDEX to make the index case insensitive.
Other RDBMS systems do this and it is nice not to depend on users being
consistent when entering names. Consider ("albert", "Daniel", "DENNIS")
which would sort exactly opposite. Also, in a primary key field (or
unique index) it would be nice if "A" was rejected if "a" already was
in the database.

Thoughts?

Followups to hackers.

--
D'Arcy J.M. Cain <darcy(at){druid|vex}.net> | Democracy is three wolves
http://www.druid.net/darcy/ | and a sheep voting on
+1 416 424 2871 (DoD#0082) (eNTP) | what's for dinner.

Hi,

> > I have what I first thought would be a trivial problem, in that
> I require
> > the 2 VARCHAR columns in the following table to have the data stored in
> > upper case.

> 1. Make sure user_id is unique or extend the WHERE clause in
> the UPDATE rule. To explain why:

This is actually just a small test table, and the real one has quite a few
more columns, but I did mean to make user_id unique, just forgot. :)

> 2. Change the WHERE clause in the UPDATE rule to compare
> against old.user_id and add "user_id = new.user_id" to
> the SET clause. Otherwise it would not be possible to
> change the user_id because this thrown away by the rule.

The thinking behind it was that user_id shouldn't be able changed but I
accidentally neglected to mention that.

> > 2) Users can still enter data straight into test_table in lower case
> > bypassing the "rules"

> Not necessarily. Since v6.4 rule actions (in contrast to
> triggers up to now) inherit the access permissions of the
> owner of the relation they're fired on.

Ahh, I see. I thought that the rule actions used the current users access
permissions, not the owners. That's much handier, thanks.

> In addition to that, consider the case you really don't want
> once given user_id's ever to change. Nor you like them to be
> ever reused. But they should disappear on DELETE.
>
> CREATE TABLE test_table (user_id int,
> name varchar(10),
> pass varchar(10),
> alive bool);
>

And that's a great way of doing what I was going to start looking at next.
:)

> The Postgres rewrite rule system is the most powerful way to
> do that.

Thanks very much for your time and comments here. It's certainly made
things clearer.

Thanks again,

---[ Neil Burrows ]-----------------------------------------------------
E-mail: neil(dot)burrows(at)gssec(dot)bt(dot)co(dot)uk British Telecom Plc.
: neil(at)pawprint(dot)co(dot)uk Glasgow Engineering Centre
Web : http://www.remo.demon.co.uk/ Highburgh Rd. Glasgow UK
-----------< Any views expressed are not those of my employer >-----------

D'Arcy J.M. Cain wrote:
>
> This makes me think of two features missing in PostgreSQL that I would
> love to see. I know it's probably to late to think about it now for
> 6.5 but I wonder what others think about this.
>
> First, as suggested above, how about an option to automatically convert
> data to upper case on entry? I realize that triggers can do the job but
> it seems to be needed often enough that putting it into the definition
> for the field seems useful. I guess a lower option would make sense too.

These could probably be implemened more effectively using rules. Having
the
rules generated automatically for simple cases would of course be nice,
but a warning at least should be given to user about creating the rule,
like it's currently done with primary key.

Or maybe it would be better to support virtual fields, like this :

create table people(
first_name varchar(25),
last_name varchar(25),
upper_first_name VIRTUAL upper(first_name),
upper_last_name VIRTUAL upper(last_name),
full_name VIRTUAL (upper_first_name || ' ' || upper_last_name)
primary key
);

and then untangle this in the backend and create required rules and
indexes automatically ?

> Second, an option to CREATE INDEX to make the index case insensitive.

If you have this option on idex, how do you plan to make sure that the
index is actually used ?

It may be better to do it explicitly -

1. create index on upper(field)

2. use where upper(field) = 'MYDATA'

---------------
Hannu

>
> D'Arcy J.M. Cain wrote:
> >
> > This makes me think of two features missing in PostgreSQL that I would
> > love to see. I know it's probably to late to think about it now for
> > 6.5 but I wonder what others think about this.
> >
> > First, as suggested above, how about an option to automatically convert
> > data to upper case on entry? I realize that triggers can do the job but
> > it seems to be needed often enough that putting it into the definition
> > for the field seems useful. I guess a lower option would make sense too.
>
> These could probably be implemened more effectively using rules. Having
> the
> rules generated automatically for simple cases would of course be nice,
> but a warning at least should be given to user about creating the rule,
> like it's currently done with primary key.

No it can't.

Such a rule would look like

CREATE RULE xxx AS ON INSERT TO this_table
DO INSTEAD INSERT INTO this_table ...

The rule system will be triggerd on an INSERT INTO
this_table, rewrite and generate another parsetree that is an
INSERT INTO this_table, which is recursively rewritten again
applying rule xxx...

That's an endless recursion. A rule can never do the same
operation to a table it is fired for.

The old pre-Postgres95 university version (Postgres release
4.2) had the possibility to define rules that UPDATE NEW.
They where buggy and didn't worked sometimes at all. Instead
of fixing them, this functionality got removed when Postgres
became 95 :-(

Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck(at)debis(dot)com (Jan Wieck) #

Jan Wieck wrote:
>
> > These could probably be implemened more effectively using rules. Having
> > the
> > rules generated automatically for simple cases would of course be nice,
> > but a warning at least should be given to user about creating the rule,
> > like it's currently done with primary key.
>
> No it can't.
>
> Such a rule would look like
>
> CREATE RULE xxx AS ON INSERT TO this_table
> DO INSTEAD INSERT INTO this_table ...
>
> The rule system will be triggerd on an INSERT INTO
> this_table, rewrite and generate another parsetree that is an
> INSERT INTO this_table, which is recursively rewritten again
> applying rule xxx...
>
> That's an endless recursion. A rule can never do the same
> operation to a table it is fired for.

But when doing that at the table creation time, then the table can
actually
be defined as a view on storage table and rules for insert update and
delete
be defined for this view that do the actual data manipulation on the
storage table.

Or is the rule system currently not capable for this ?

When some field is changed to UPPER-ONLY status using alter table, the
table
could be renamed to staorage table and all the rules be created ?

And the other question - what is the status of ALTER TABLE commands -
can we add/remove/disable constraints without recreating the table ?

Is constraint and index disabling supported at all ?

-------------------
Hannu

> But when doing that at the table creation time, then the table can
> actually
> be defined as a view on storage table and rules for insert update and
> delete
> be defined for this view that do the actual data manipulation on the
> storage table.

That's IMHO a too specific case to do it generally with the
rule system. Should be some kind of constraint handled by
the parser in putting an UPPER() func node around the
targetlist expression.

There could be more general support implemented, in that a
user can allways tell that a custom function should be called
with the result of the TLE-expr before the value is dropped
into the tuple on INSERT/UPDATE.

Jan

--

#======================================================================#
# It's easier to get forgiveness for being wrong than for being right. #
# Let's break this rule - forgive me. #
#======================================== jwieck(at)debis(dot)com (Jan Wieck) #