Hello 2010/11/15 Itagaki Takahiro <itagaki.takah...@gmail.com>: > On Fri, Nov 12, 2010 at 00:02, Itagaki Takahiro > <itagaki.takah...@gmail.com> wrote: >> Postgres supports ARRAY data types well, but there are some >> more array functions in the SQL standard. Also, the standard >> has MULTISET data type, that is an unordered array. > > Here is a WIP patch for multiset function supports. Note that multiset > types are not added in the patch; it just adds functions and syntax. > Arguments or result types of those functions are anyarray rather than > anymultiset. The result type is always flatten into on-dimensional > array because some functions requires per-element operations; I'm not > sure how we should treat trim_array( 2D 3x3 array, 2 elements ). So, > it is treated as trim_array( 9 elements array, 2 elements ) in the patch. > > The SQL standard defines special syntax for multiset. I added four > unreserved keywords for them; A, MEMBER, MULTISET, and SUB. > (I don't like such ad-hoc syntax, but it is the standard...) > Some of the new expressions are just syntactic sugar for existing > other expressions or new functions. For example, "$1 MEMBER OF $2" is > expanded to "$1 = ANY ($2)" and "$1 IS A SET" to "multiset_is_a_set($1)". > > I have not researched the spec yet enough, especially NULLs in collections. > I'll continue to check the details. > > BTW, some of the intermediate products to implement those features might > be useful if exported. like array_sort() and array_unique(). If there is > demand, I'll add those functions, too. > > Any comments for the approach or detailed features? >
I has not a standard, so I can't to speak about conformance with standard, but I must to say, so these functionality should be extremely useful for plpgsql programming. You can see samples a some functions on the net for array sorting, for reduce a redundant values via SQL language. I am sure, so implementation in C will be much faster. Maybe can be useful to implement a searching on sorted array. You can hold a flag if multiset is sorted or not. Regards Pavel Stehule > === New features === > - [FUNCTION] cardinality(anyarray) => integer > - [FUNCTION] trim_array(anyarray, nTrimmed integer) => anyarray > - [FUNCTION] element(anyarray) => anyelement > - [SYNTAX] $1 MEMBER OF $2 --> $1 = ANY ($2) > - [SYNTAX] $1 SUB MULTISET OF $2 --> $1 <@ $2 > - [SYNTAX] $1 IS A SET --> multiset_is_a_set($1) > - [SYNTAX] $1 MULTISET UNION [ALL | DISTINCT] $2 --> > multiset_union($1, $2, all?) > - [SYNTAX] $1 MULTISET INTERSECT [ALL | DISTINCT] $2 --> > multiset_intersect($1, $2, all?) > - [SYNTAX] $1 MULTISET EXCEPT [ALL | DISTINCT] $2 --> > multiset_except($1, $2, all?) > - [AGGREGATE] collect(anyelement) => anyarray --> same as array_agg() > - [AGGREGATE] fusion(anyarray) => anyarray > - [AGGREGATE] intersection(anyarray) => anyarray > > -- > Itagaki Takahiro > > > -- > Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) > To make changes to your subscription: > http://www.postgresql.org/mailpref/pgsql-hackers > > -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
