Обсуждение: How to get the max on a char column?
Hi ! I am quite confused of the results on a SELECT max... My environment: Conectiva Linux 10, PostgreSQL 7.4.6 (compiled from the sources) My problem is the "select max(id) FROM test" the result is 20 but the right is 1020. Is this a BUG or I am crazy ?? Cheers, Rodrigo Carvalhaes The SQL... teste=# CREATE TABLE test ( id char(15), name char(80) ); CREATE TABLE teste=# \d test Table "public.test" Column | Type | Modifiers --------+---------------+----------- id | character(15) | name | character(80) | teste=# INSERT INTO test VALUES ( '10', 'luidgi'); INSERT 15303727 1 teste=# INSERT INTO test VALUES ( '20', 'luis'); INSERT 15303728 1 teste=# INSERT INTO test VALUES ( '1010', 'ruan'); INSERT 15303729 1 teste=# INSERT INTO test VALUES ( '1020', 'lion'); INSERT 15303730 1 teste=# SELECT * FROM test; id | name -----------------+---------------------------------------------------------------------------------- 10 | luidgi 20 | luis 1010 | ruan 1020 | lion (4 rows) teste=# SELECT max(id) FROM test; max ----- 20 (1 row) teste=# select max(id) FROM test; max ----- 20 (1 row) ---------------------------(end of broadcast)--------------------------- TIP 1: subscribe and unsubscribe commands go to majordomo@postgresql.org
--- Rodrigo Carvalhaes <grupos@carvalhaes.net> wrote:
> Hi !
>
> I am quite confused of the results on a SELECT
> max...
>
> My environment:
> Conectiva Linux 10, PostgreSQL 7.4.6 (compiled from
> the sources)
>
> My problem is the "select max(id) FROM test" the
> result is 20 but the
> right is 1020. Is this a BUG or I am crazy ??
For a char() column, '20' is the maximum of the values
that you have inserted, because the comparison is
text-based, not numeric. If you want numeric sorting,
you will need to cast the value, like:
select max(cast(id as integer)) from test;
I'm not sure offhand whether in fact a direct cast
from char() to integer is available; you may need to
cast to "text" first.
But if you expect to be able to sort numerically, why
are you not using a numeric datatype?
>
> Cheers,
>
> Rodrigo Carvalhaes
>
> The SQL...
>
> teste=# CREATE TABLE test ( id char(15), name
> char(80) );
> CREATE TABLE
> teste=# \d test
> Table "public.test"
> Column | Type | Modifiers
> --------+---------------+-----------
> id | character(15) |
> name | character(80) |
>
> teste=# INSERT INTO test VALUES ( '10', 'luidgi');
> INSERT 15303727 1
> teste=# INSERT INTO test VALUES ( '20', 'luis');
> INSERT 15303728 1
> teste=# INSERT INTO test VALUES ( '1010', 'ruan');
> INSERT 15303729 1
> teste=# INSERT INTO test VALUES ( '1020', 'lion');
> INSERT 15303730 1
> teste=# SELECT * FROM test;
> id |
> name
>
-----------------+----------------------------------------------------------------------------------
>
>
> 10 | luidgi
> 20 | luis
> 1010 | ruan
> 1020 | lion
> (4 rows)
>
> teste=# SELECT max(id) FROM test;
> max
> -----
> 20
> (1 row)
>
> teste=# select max(id) FROM test;
> max
> -----
> 20
> (1 row)
>
>
>
>
>
> ---------------------------(end of
> broadcast)---------------------------
> TIP 1: subscribe and unsubscribe commands go to
> majordomo@postgresql.org
>
>
> ---------------------------(end of
> broadcast)---------------------------
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Dear Jeff, Thank you for your help. I tried : select max((id::text)::integer) from test; and works perfectly! Greetings from Brazil! Rodrigo Carvalhaes Jeff Eckermann wrote: >--- Rodrigo Carvalhaes <grupos@carvalhaes.net> wrote: > > > >>Hi ! >> >>I am quite confused of the results on a SELECT >>max... >> >>My environment: >>Conectiva Linux 10, PostgreSQL 7.4.6 (compiled from >>the sources) >> >>My problem is the "select max(id) FROM test" the >>result is 20 but the >>right is 1020. Is this a BUG or I am crazy ?? >> >> > >For a char() column, '20' is the maximum of the values >that you have inserted, because the comparison is >text-based, not numeric. If you want numeric sorting, >you will need to cast the value, like: > >select max(cast(id as integer)) from test; > >I'm not sure offhand whether in fact a direct cast >from char() to integer is available; you may need to >cast to "text" first. > >But if you expect to be able to sort numerically, why >are you not using a numeric datatype? > > > >>Cheers, >> >>Rodrigo Carvalhaes >> >>The SQL... >> >>teste=# CREATE TABLE test ( id char(15), name >>char(80) ); >>CREATE TABLE >>teste=# \d test >> Table "public.test" >>Column | Type | Modifiers >>--------+---------------+----------- >>id | character(15) | >>name | character(80) | >> >>teste=# INSERT INTO test VALUES ( '10', 'luidgi'); >>INSERT 15303727 1 >>teste=# INSERT INTO test VALUES ( '20', 'luis'); >>INSERT 15303728 1 >>teste=# INSERT INTO test VALUES ( '1010', 'ruan'); >>INSERT 15303729 1 >>teste=# INSERT INTO test VALUES ( '1020', 'lion'); >>INSERT 15303730 1 >>teste=# SELECT * FROM test; >> id | >> name >> >> >> >-----------------+---------------------------------------------------------------------------------- > > >>10 | luidgi >>20 | luis >>1010 | ruan >>1020 | lion >>(4 rows) >> >>teste=# SELECT max(id) FROM test; >>max >>----- >>20 >>(1 row) >> >>teste=# select max(id) FROM test; >>max >>----- >>20 >>(1 row) >> >> >> >> >> >>---------------------------(end of >>broadcast)--------------------------- >>TIP 1: subscribe and unsubscribe commands go to >>majordomo@postgresql.org >> >> >>---------------------------(end of >>broadcast)--------------------------- >>TIP 1: subscribe and unsubscribe commands go to >>majordomo@postgresql.org >> >> >> > > > > >__________________________________ >Do you Yahoo!? >Meet the all-new My Yahoo! - Try it today! >http://my.yahoo.com > > > >