Re: [HACKERS] Reference Manual]

> 2. - Seems that optional ALL keyword of UNION doesn't work.
>      The following query prints always the same result with and without
>      the ALL clause.
>
> *    UNION of two tables:
>
> mytable:            yourtable:
>          id|name               id|name
>          --+------             --+------
>           1|Smith               1|Soares
>           2|Jones               2|Panini
>           3|Soares
>
>
> SELECT mytable.id, mytable.name
> FROM mytable
> WHERE mytable.name LIKE 'S%'
>    UNION
>        SELECT yourtable.id, yourtable.name
>        FROM yourtable
>        WHERE yourtable.name LIKE 'S%';
>
> this is the result even if I don't specify ALL.
>                      id|name
>                      --+------
>                       1|Smith
>                       1|Soares
>                       3|Soares

The second column is duplicate, but the first is not.  It looks at all
columns to determine duplicates.

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