* Grzegorz Jaśkiewicz:
> 2010/11/24 Florian Weimer <fweimer@bfk.de>:
>> * Grzegorz Jaśkiewicz:
>>
>>> just never use SELECT *, but always call columns by names. You'll
>>> avoid having to depend on the order of columns, which is never
>>> guaranteed, even if the table on disk is one order, the return columns
>>> could be in some other.
>>
>> This can't be true because several SQL features rely on deterministic
>> column order. Here's an example:
>>
>> SELECT 1 AS a, 2 AS b UNION SELECT 3 AS b, 4 AS a;
>>
>> a | b
>> ---+---
>> 1 | 2
>> 3 | 4
>> (2 rows)
> Yes, most DBs do a good job to keep it consistent, but they don't have
> to. So unless you specify column names explicitly (like you did in the
> example above), there's no guarantees.
If the database looked at the column names, the result would be
(1, 2), (4, 3), not (1, 2), (3, 4).
--
Florian Weimer <fweimer@bfk.de>
BFK edv-consulting GmbH http://www.bfk.de/
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