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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