Thread: More outdated examples
This example in User's Guide section 7.2 doesn't work anymore at all: tgl=> select @ text '-4.5' as "abs";abs -----4.5 (1 row) What really happens is this: => select @ text '-4.5' as "abs"; ERROR: Unable to identify a prefix operator '@' for type 'text' You may need to add parentheses or an explicit cast Again, delete or new example? -- Peter Eisentraut peter_e@gmx.net
I can find no suitable replacement for this example. Can anyone else? --------------------------------------------------------------------------- Peter Eisentraut wrote: > This example in User's Guide section 7.2 doesn't work anymore at all: > > tgl=> select @ text '-4.5' as "abs"; > abs > ----- > 4.5 > (1 row) > > What really happens is this: > > => select @ text '-4.5' as "abs"; > ERROR: Unable to identify a prefix operator '@' for type 'text' > You may need to add parentheses or an explicit cast > > Again, delete or new example? > > -- > Peter Eisentraut peter_e@gmx.net > > > ---------------------------(end of broadcast)--------------------------- > TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073
Bruce Momjian <pgman@candle.pha.pa.us> writes:
> I can find no suitable replacement for this example. Can anyone else?
> Peter Eisentraut wrote:
>> This example in User's Guide section 7.2 doesn't work anymore at all:
>>
>> tgl=> select @ text '-4.5' as "abs";
Both of the examples in this section have been obsoleted by our recent
elimination of a lot of implicit casts. This one would still work if
text-to-float8 were an implicit cast, but it's not anymore. Also,
though the second one still acts as described, the reason given for it
in the text is wrong: the system is not unable to choose among multiple
alternatives. Rather, it finds *no* alternatives, again because the
text-to-various-int-types casts are no longer implicit.
The closest similar cases that I can find for the first example are not
good replacements because they are also slated for destruction :-(.
Basically, I see us moving away from the preferred-type mechanism, and
perhaps eliminating it entirely soon.
I'd just remove the whole of Example 7.3, I think. The mechanisms are
still there, for now, but they are not invoked in any standard cases.
regards, tom lane
The following applied patch removes the section Tom thought wasn't needed anymore. --------------------------------------------------------------------------- Tom Lane wrote: > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > I can find no suitable replacement for this example. Can anyone else? > > > Peter Eisentraut wrote: > >> This example in User's Guide section 7.2 doesn't work anymore at all: > >> > >> tgl=> select @ text '-4.5' as "abs"; > > Both of the examples in this section have been obsoleted by our recent > elimination of a lot of implicit casts. This one would still work if > text-to-float8 were an implicit cast, but it's not anymore. Also, > though the second one still acts as described, the reason given for it > in the text is wrong: the system is not unable to choose among multiple > alternatives. Rather, it finds *no* alternatives, again because the > text-to-various-int-types casts are no longer implicit. > > The closest similar cases that I can find for the first example are not > good replacements because they are also slated for destruction :-(. > Basically, I see us moving away from the preferred-type mechanism, and > perhaps eliminating it entirely soon. > > I'd just remove the whole of Example 7.3, I think. The mechanisms are > still there, for now, but they are not invoked in any standard cases. > > regards, tom lane > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001 + If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania 19073 Index: doc/src/sgml/typeconv.sgml =================================================================== RCS file: /cvsroot/pgsql-server/doc/src/sgml/typeconv.sgml,v retrieving revision 1.27 diff -c -c -r1.27 typeconv.sgml *** doc/src/sgml/typeconv.sgml 13 Mar 2003 01:30:29 -0000 1.27 --- doc/src/sgml/typeconv.sgml 19 Mar 2003 21:17:32 -0000 *************** *** 403,459 **** </para> </example> - <example> - <title>Absolute-Value and Factorial Operator Type Resolution</title> - - <para> - The <productname>PostgreSQL</productname> operator catalog has several - entries for the prefix operator <literal>@</>, all of which implement - absolute-value operations for various numeric data types. One of these - entries is for type <type>float8</type>, which is the preferred type in - the numeric category. Therefore, <productname>PostgreSQL</productname> - will use that entry when faced with a non-numeric input: - <screen> - SELECT @ '-4.5' AS "abs"; - abs - ----- - 4.5 - (1 row) - </screen> - Here the system has performed an implicit conversion from <type>text</type> to <type>float8</type> - before applying the chosen operator. We can verify that <type>float8</type> and - not some other type was used: - <screen> - SELECT @ '-4.5e500' AS "abs"; - - ERROR: Input '-4.5e500' is out of range for float8 - </screen> - </para> - - <para> - On the other hand, the postfix operator <literal>!</> (factorial) - is defined only for integer data types, not for <type>float8</type>. So, if we - try a similar case with <literal>!</>, we get: - <screen> - SELECT '20' ! AS "factorial"; - - ERROR: Unable to identify a postfix operator '!' for type 'text' - You may need to add parentheses or an explicit cast - </screen> - This happens because the system can't decide which of the several - possible <literal>!</> operators should be preferred. We can help - it out with an explicit cast: - <screen> - SELECT CAST('20' AS int8) ! AS "factorial"; - - factorial - --------------------- - 2432902008176640000 - (1 row) - </screen> - </para> - </example> - </sect1> <sect1 id="typeconv-func"> --- 403,408 ----
The specific case that Tom complained about wasn't even in the latest documentation sources anymore. I think the patch should be reverted. Bruce Momjian writes: > > The following applied patch removes the section Tom thought wasn't > needed anymore. > > --------------------------------------------------------------------------- > > Tom Lane wrote: > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > > I can find no suitable replacement for this example. Can anyone else? > > > > > Peter Eisentraut wrote: > > >> This example in User's Guide section 7.2 doesn't work anymore at all: > > >> > > >> tgl=> select @ text '-4.5' as "abs"; > > > > Both of the examples in this section have been obsoleted by our recent > > elimination of a lot of implicit casts. This one would still work if > > text-to-float8 were an implicit cast, but it's not anymore. Also, > > though the second one still acts as described, the reason given for it > > in the text is wrong: the system is not unable to choose among multiple > > alternatives. Rather, it finds *no* alternatives, again because the > > text-to-various-int-types casts are no longer implicit. > > > > The closest similar cases that I can find for the first example are not > > good replacements because they are also slated for destruction :-(. > > Basically, I see us moving away from the preferred-type mechanism, and > > perhaps eliminating it entirely soon. > > > > I'd just remove the whole of Example 7.3, I think. The mechanisms are > > still there, for now, but they are not invoked in any standard cases. > > > > regards, tom lane > > > > -- Peter Eisentraut peter_e@gmx.net
OK, readded. Thanks. --------------------------------------------------------------------------- Peter Eisentraut wrote: > The specific case that Tom complained about wasn't even in the latest > documentation sources anymore. I think the patch should be reverted. > > Bruce Momjian writes: > > > > > The following applied patch removes the section Tom thought wasn't > > needed anymore. > > > > --------------------------------------------------------------------------- > > > > Tom Lane wrote: > > > Bruce Momjian <pgman@candle.pha.pa.us> writes: > > > > I can find no suitable replacement for this example. Can anyone else? > > > > > > > Peter Eisentraut wrote: > > > >> This example in User's Guide section 7.2 doesn't work anymore at all: > > > >> > > > >> tgl=> select @ text '-4.5' as "abs"; > > > > > > Both of the examples in this section have been obsoleted by our recent > > > elimination of a lot of implicit casts. This one would still work if > > > text-to-float8 were an implicit cast, but it's not anymore. Also, > > > though the second one still acts as described, the reason given for it > > > in the text is wrong: the system is not unable to choose among multiple > > > alternatives. Rather, it finds *no* alternatives, again because the > > > text-to-various-int-types casts are no longer implicit. > > > > > > The closest similar cases that I can find for the first example are not > > > good replacements because they are also slated for destruction :-(. > > > Basically, I see us moving away from the preferred-type mechanism, and > > > perhaps eliminating it entirely soon. > > > > > > I'd just remove the whole of Example 7.3, I think. The mechanisms are > > > still there, for now, but they are not invoked in any standard cases. > > > > > > regards, tom lane > > > > > > > > > -- > Peter Eisentraut peter_e@gmx.net > > > -- Bruce Momjian | http://candle.pha.pa.us pgman@candle.pha.pa.us | (610) 359-1001+ If your life is a hard drive, | 13 Roberts Road + Christ can be your backup. | Newtown Square, Pennsylvania19073