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Re: can someone explain confusing array indexing nomenclature

From: Achilleas Mantzios <achill(at)matrix(dot)gatewaynet(dot)com>
To: pgsql-sql(at)postgresql(dot)org
Subject: Re: can someone explain confusing array indexing nomenclature
Date: 2007-02-15 10:24:12
Message-ID: 200702151224.12455.achill@matrix.gatewaynet.com (view raw or flat)
Thread:
Lists: pgsql-sql
Στις Τετάρτη 14 Φεβρουάριος 2007 21:31, ο/η chrisj έγραψε:
> given the following table:
>
> protocal2=> select * from sal_emp ;
>  name  |      pay_by_quarter       |                 schedule
> -------+---------------------------+---------------------------------------
>---- Bill  | {10000,10000,10000,10000} |
> {{meeting,lunch},{training,presentation}}
>  Carol | {20000,25000,25000,25000} |
> {{breakfast,consulting},{meeting,lunch}}
> (2 rows)
>
> why do the following two queries yield different results??
>
> protocal2=> SELECT schedule[1][2] FROM sal_emp WHERE name = 'Bill';
>  schedule
> ----------
>  lunch
> (1 row)
>
> protocal2=> SELECT schedule[1:1][2] FROM sal_emp WHERE name = 'Bill';
>      schedule
> -------------------
>  {{meeting,lunch}}
> (1 row)

The [n:m] notation denotes a slice of the array (not element).
So schedule[1][2] is the Array element on 2nd col of 1st row, 
while schedule[1:1][2] could mean
the second row of the subarray schedule[1:1][1:2].
So these two are foundamentally different things.
In my 7.4 even if you gave 
SELECT schedule[1:1][888] FROM sal_emp WHERE name = 'Bill';
you would still get  {{meeting,lunch}} as a result.
(Right or wrong is another story).
Anyway the first time you query for a "text",
the second time you query for a "text[]", so you should expect
different results.
-- 
Achilleas Mantzios

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