| From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
|---|---|
| To: | Robert Haas <robertmhaas(at)gmail(dot)com> |
| Cc: | Greg Stark <stark(at)mit(dot)edu>, Alvaro Herrera <alvherre(at)2ndquadrant(dot)com>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, wangshuo(at)highgo(dot)com(dot)cn, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Re: [HACKERS] Re: [HACKERS] Re: [HACKERS] Is it necessary to rewrite table while increasing the scale of datatype numeric？ |
| Date: | 2013-09-06 18:47:02 |
| Message-ID: | 2496.1378493222@sss.pgh.pa.us |
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| Lists: | pgsql-hackers |
Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> Sure, but the point is that 5.0000 is not the same as 5.000 today. If
> you start whacking this around you'll be changing that behavior, I
> think.
Yeah. And please note that no matter what the OP may think, a lot of
people *do* consider that there's a useful distinction between 5.000
and 5.0000 --- it might indicate the number of significant digits in
a measurement, for example. I do not see us abandoning that just to make
certain cases of ALTER TABLE faster.
There was some upthread discussion about somehow storing the scale info
at the column level rather than the individual-datum level. If we could
do that, then it'd be possible to make this type of ALTER TABLE fast.
However, the work involved to do that seems enormously out of proportion
to the benefit, mainly because there just isn't any convenient way to
trace a Datum to its source column, even assuming it's got one.
regards, tom lane
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