Re: Serial Updating

am Sun, dem 03.09.2006, um 14:24:41 -0700 mailte Bob Pawley folgendes:
> I have a column that I wish to use to designate loop numbers.
>
> A loop number is composed of a letter (F for flow, T for temperatures etc.)
> followed by a sequence number starting at one and ending with the last loop.
>
> The loop numbers will appear as F-1, T-2 and so on.
>
> I seem to have no problem designating the column with the appropriate letters.
>
> However, I haven't a clue how to add the numerical portion - or if it is
> even possible.

I'n not sure if i understand you correctly, but perhaps this example
will be helpful for you:

test=# select * from foo;
col1
------
a
b
a
c
a
(5 rows)

test=*# create sequence s1;
CREATE SEQUENCE
test=*# create sequence s2;
CREATE SEQUENCE
test=*# select col1, case when col1 = 'a' then nextval('s1') when col1 ='b' then nextval('s2') else 0 end from foo;
col1 | case
------+------
a | 1
b | 1
a | 2
c | 0
a | 3
(5 rows)

-- or, with the value from col1:

test=*# rollback;
ROLLBACK
test=# create sequence s1;
CREATE SEQUENCE
test=*# create sequence s2;
CREATE SEQUENCE
test=*# select col1, col1 || '-' || case when col1 = 'a' then nextval('s1') when col1 ='b' then nextval('s2') else 0 end from foo;
col1 | ?column?
------+----------
a | a-1
b | b-1
a | a-2
c | c-0
a | a-3

Read more about conditional expressions:
http://www.postgresql.org/docs/8.1/interactive/functions-conditional.html#AEN12589
and about sequences:
http://www.postgresql.org/docs/8.1/interactive/sql-createsequence.html

HTH, Andreas
--
Andreas Kretschmer
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