Обсуждение: how to generate a list of distinct scalar values from a column which type is array

Dear all,

given a column which type is for instance varchar(20)[], is it possible via SQL to generate the list of distinct scalar values?


e.g.:
             col1
row 1: (aaa, bb, c)
row 2: (dddd, eeee)
row 3: (aaa, eeee)

the query should return:

aaa
bb
c
dddd
eeee

if not, I guess the approach is to use stored procedure. Any code snippet/suggestion?

Thanks, Sergio

On Thu, Feb 22, 2007 at 12:38:50PM +0100, Sergio Andreozzi wrote:
> Dear all,
>
> given a column which type is for instance varchar(20)[],

This is almost never a good design.  If you must have an interface
like that, make it VIEW over an aggregate, which you can make
writeable.

> is it possible via SQL to generate the list of distinct scalar
> values?

Yes, but you should fix your design :)

CREATE TABLE foo (ft TEXT[]);

COPY foo(ft) FROM stdin;
{aaa,bb,c}
{dddd,eeee}
{aaa,eeee}
\.

SELECT DISTINCT ft[i]
FROM (
    SELECT ft,
        generate_series(
            array_lower(ft,1),
            array_upper(ft,1)
        ) AS i
    FROM foo
) AS bar;

So, yes, you can do it, and no, you shouldn't.

Cheers,
D
--
David Fetter <david@fetter.org> http://fetter.org/
phone: +1 415 235 3778        AIM: dfetter666
                              Skype: davidfetter

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