Re: Why extract( ... from timestamp ) is not immutable?

On 2012-01-25, hubert depesz lubaczewski <depesz(at)depesz(dot)com> wrote:
> On Wed, Jan 25, 2012 at 02:07:40PM -0800, Adrian Klaver wrote:
>> Finally dawned on me. When you use 'at time zone' on a timestamp
>> with tz it strips the tz which then allows the value to be indexed
>> because:
>>
>> -[ RECORD 5 ]-------+-------------------------------------------------------------------------
>> Schema | pg_catalog
>> Name | date_part
>> Result data type | double precision
>> Argument data types | text, timestamp without time zone
>> Type | normal
>> Volatility | immutable
>> Owner | postgres
>> Language | internal
>> Source code | timestamp_part
>> Description | extract field from timestamp
>
> yes, but it is not correct - the value is actually stable, and not
> immutable.

it's immutable for all date parts except "epoch".

epoch is backwards to the other date parts.
immutable for timestamptz and stable for timestamp

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