database/postgres
1
0
Fork 0
mirror of https://github.com/postgres/postgres.git synced 2025-07-27 12:41:57 +03:00
Code Activity

Update of contrib stuff from massimo.

Browse Source
This commit is contained in:
Bruce Momjian
1997-11-05 21:38:25 +00:00
parent 5aaf00f3f3
commit 951986c550
33 changed files with 2547 additions and 578 deletions
Download Patch File Download Diff File Expand all files Collapse all files

56
contrib/array/array_iterator.doc
View File

@ -1,26 +1,44 @@
From: Massimo Dal Zotto <dz@cs.unitn.it>
Date: Mon, 6 May 1996 01:03:37 +0200 (MET DST)
Subject: [PG95]: new operators for arrays
Array iterator functions, by Massimo Dal Zotto <dz@cs.unitn.it>
- -----BEGIN PGP SIGNED MESSAGE-----
This loadable module defines a new class of functions which take
an array and a scalar value, iterate a scalar operator over the
elements of the array and the value, and compute a result as
the logical OR or AND of the iteration results.
For example array_int4eq returns true if some of the elements
of an array of int4 is equal to the given value:
Hi,
array_int4eq({1,2,3}, 1) --> true
array_int4eq({1,2,3}, 4) --> false
I have written an extension to Postgres95 which allows to use qualification
clauses based on the values of single elements of arrays.
For example I can now select rows having some or all element of an array
If we have defined T array types and O scalar operators we can
define T x O x 2 array functions, each of them has a name like
"array_[all_]<basetype><operation>" and takes an array of type T
iterating the operator O over all the elements. Note however
that some of the possible combination are invalid, for example
the array_int4_like because there is no like operator for int4.
We can then define new operators based on these functions and use
them to write queries with qualification clauses based on the
values of some of the elements of an array.
For example to select rows having some or all element of an array
attribute equal to a given value or matching a regular expression:
select * from t where t.foo *= 'bar';
select * from t where t.foo **~ '^ba[rz]';
create table t(id int4[], txt text[]);
The scheme is quite general, each operator which operates on a base type can
be iterated over the elements of an array. It seem to work well but defining
each new operators requires writing a different C function. Furthermore in
each function there are two hardcoded OIDs which reference a base type and
a procedure. Not very portable. Can anyone suggest a better and more portable
way to do it ? Do you think this could be a useful feature for next release ?
Here is my code, it can be compiled and loaded as a dynamic module without
need to recompile the backend. I have defined only the few operators I needed,
the list can be extended. Feddback is welcome.
-- select tuples with some id element equal to 123
select * from t where t.id *= 123;
-- select tuples with some txt element matching '[a-z]'
select * from t where t.txt *~ '[a-z]';
-- select tuples with all txt elements matching '^[A-Z]'
select * from t where t.txt[1:3] **~ '^[A-Z]';
The scheme is quite general, each operator which operates on a base type
can be iterated over the elements of an array. It seem to work well but
defining each new operators requires writing a different C function.
Furthermore in each function there are two hardcoded OIDs which reference
a base type and a procedure. Not very portable. Can anyone suggest a
better and more portable way to do it ?
See also array_iterator.sql for an example on how to use this module.