mirror of
https://github.com/postgres/postgres.git
synced 2025-10-29 22:49:41 +03:00
5cabcfccce
array header, and to compute sizing and alignment of array elements the same way normal tuple access operations do --- viz, using the tupmacs.h macros att_addlength and att_align. This makes the world safe for arrays of cstrings or intervals, and should make it much easier to write array-type-polymorphic functions; as examples see the cleanups of array_out and contrib/array_iterator. By Joe Conway and Tom Lane.
50 lines
2.1 KiB
Plaintext
50 lines
2.1 KiB
Plaintext
Array iterator functions, by Massimo Dal Zotto <dz@cs.unitn.it>
|
|
Copyright (C) 1999, Massimo Dal Zotto <dz@cs.unitn.it>
|
|
|
|
This software is distributed under the GNU General Public License
|
|
either version 2, or (at your option) any later version.
|
|
|
|
|
|
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:
|
|
|
|
array_int4eq({1,2,3}, 1) --> true
|
|
array_int4eq({1,2,3}, 4) --> false
|
|
|
|
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:
|
|
|
|
create table t(id int4[], txt text[]);
|
|
|
|
-- 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 operator requires writing a different C function.
|
|
This is tedious, and error-prone since one must take care that the correct
|
|
datatypes are associated with the selected underlying function.
|
|
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.
|