Re: BUG #14919: Invalid column in sub select is still a valid select

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От Marko Tiikkaja
Тема Re: BUG #14919: Invalid column in sub select is still a valid select
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Msg-id CAL9smLCcQZo8pZcF0XNxkus3Y_3zprdXJXNMi7hx7XLS3EOCYw@mail.gmail.com
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Ответ на Re: BUG #14919: Invalid column in sub select is still a valid select  (Tanes Sriviroolchai <tanes@siamscan.net>)
Ответы Re: BUG #14919: Invalid column in sub select is still a valid select  (Tanes Sriviroolchai <tanes@siamscan.net>)
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On Mon, Nov 20, 2017 at 3:49 PM, Tanes Sriviroolchai <tanes@siamscan.net> wrote:
Really? The fact that 1st statement doen't end in exception throwing is ok? (While the same sub select executes with exception throwing.)

select * from a where id=(select id from b where descr='A');

Because "b" doesn't have a column called "id", this is the same as:

  select * from a where id=(select a.id from b where descr='A');

and that's a valid, though slightly silly, query.  In other words, you accidentally wrote a correlated subquery.  Some people consider it good practice to qualify column references with the name of the table when there's more than one column in scope.  If you had written:

  select * from a where id=(select b.id from b where b.descr='A');

you would have noticed that you made a mistake, due to the exception this query raises.


.m

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