[HACKERS] How to deal with order by, group by, distinct for user-defined types

[Ruey-Lung Hsiao]

Hi,
  I implemented a user-defined type, say X, and when I want to do the 
following queries, Postgresql will complain

CREATE TABLE Table1 ( id integer, object X );
SELECT X, count(*) from Table1
GROUP BY X;
ERROR:  could not identify an ordering operator for type X
HINT:  Use an explicit ordering operator or modify the query.
  My question is: how do I find or define ordering operators for my 
user-defined type?

Thanks.
Ruey-Lung Hsiao
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[HACKERS] How to check the postgresql version

[Ruey-Lung Hsiao]

Hi,
  Sorry if this problem seems stupid but I would appreciate it if 
someone helps.

  I've been implementing several user-defined types and their 
corresponding GiST index in postgresql 7.4.3. They worked well. However, 
I have noticed there are several changes in SPI functions and their 
parameters in 8.0beta. I want to be able to compile my codes in 
Postgresql 7.4.X and 8.0.X, so the only way to do that is to use the C 
preprocessor directives to check PG_VERSION (defined in pg_config.h).

  My problem is: I can't find a way to compare strings in C 
preprocessor directive since PG_VERSION is defined as something like 
"7.4.3" or "7.4.6". I ultimately want to do the following things:

#if PG_VERSION starts with "8.X"
 ... call 8.0 compatible functions
#else
 ... call 7.4.x compatible functions
#endif
  Could anyone tell me how to do this kind of version check task? 
Thank you very much.

Ruey-Lung Hsiao
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[HACKERS] "no snapshot has been set" error

[Ruey-Lung Hsiao]

Hi all,
  I encountered a problem when I'm implementing my user-defined type. 
My  user-defined type is defined as

CREATE TYPE X
(
   INTERNALLENGTH = 10
   INPUT = X_in,
   OUTPUT = X_out
);
In my X_in() function, I want to access other table to do some 
bookkeeping stuff. this table keeps track of the number of calls to 
X_in(). However, while SPI_connect() returns SPI_OK_CONNECT, whenever I 
execute SPI_exec( "SELECT count FROM XTABLE", 0), postgres stops 
executing and issues "Error: no snapshot has been set".

Does anyone here knows what happens?  Am I not allowed to use SPI 
functions in this situation?

Thank you for your advice and suggestions in advance.
Ruey-Lung Hsiao
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