问题
I found a SELECT-example on the web. When I try it in my script I get this error-message:
Specifying DISTINCT when using aggregate functions isn't reasonable - ignored. at /usr/lib/perl5/site_perl/5.10.0/SQL/Parser.pm line 496.
#!/usr/bin/perl
use warnings;
use strict;
use DBI;
my $dbh = DBI->connect( "DBI:CSV:", undef, undef, { RaiseError => 1, AutoCommit => 1 } );
my $table = 'artikel';
my $array_ref = [ [ 'a_nr', 'a_name', 'a_preis' ],
[ 12, 'Oberhemd', 39.80, ],
[ 22, 'Mantel', 360.00, ],
[ 11, 'Oberhemd', 44.20, ],
[ 13, 'Hose', 119.50, ],
];
$dbh->do( "CREATE TEMP TABLE $table AS IMPORT(?)", {}, $array_ref );
my $sth = $dbh->prepare( "SELECT DISTINCT a_name FROM $table" );
$sth->execute();
$sth->dump_results();
$dbh->disconnect();
Does SELECT DISTINCT not work with DBD::CSV or is something wrong with my script?
edit: The output is
'Oberhemd'
'Mantel'
'Oberhemd'
'Hose'
4 rows
I thought it should be
'Oberhemd'
'Mantel'
'Hose'
3 rows
Installed versions:
Perl : 5.010000 (x86_64-linux-thread-multi)
OS : linux (2.6.31)
DBI : 1.609
DBD::Sponge : 12.010002
DBD::SQLite : 1.25
DBD::Proxy : 0.2004
DBD::Gofer : 0.011565
DBD::File : 0.37
DBD::ExampleP : 12.010007
DBD::DBM : 0.03
DBD::CSV : 0.26
回答1:
Hi This is an easily reproducable bug. SELECT data_display_mask FROM test.csv returns 200 plus rows. SELECT DISTINCT data_display_mask FROM test.csv returns the warning message and same 200 rows.
If i do an awk, sort -u for unique ( values of the row ) I get 36 values, which is what I would expect.
Certainly a bug in the code.
-Kanwar
perl -V Summary of my perl5 (revision 5 version 10 subversion 0) configuration: Platform: osname=linux, osvers=2.2.24-6.2.3, archname=i686-linux-thread-multi
DBD::CSV 0.26 SQL::Parser 1.23 DBI 1.609
example:
Specifying DISTINCT when using aggregate functions isn't reasonable - ignored. at /opt/perl2exe/perl5/lib/site_perl/5.10.0/SQL/Parser.pm line 496. 87060 87060 87060 87060
SQL used is SELECT DISTINCT entry_id FROM test.csv
回答2:
Note that the message about something being not reasonable is
- Only a warning. Your script works nevertheless.
- Confusing and non-sensical: you don't use any aggregate functions.
I smell a bug in either DBD::CSV or SQL::Statement.
Edit: DISTINCT is explicitly allowed in SQL::Statement
回答3:
my $sth = $dbh->prepare("SELECT DISTINCT $attributeName1, COUNT( $attributeName2) FROM tableName GROUP BY $attributeName1, $attributeName2");
this gave me: attributeName1 and a distinct count of attributeName2
回答4:
This is an example of a more general phenomenon with DBD::CSV, namely, that it allows a lot of SQL syntax for which the meaning is silently ignored.
I have seen cases of SELECT DISTINCT that actually filter out duplicates, so the case you mention here seems a bug,
but I haven't found a way to make the DISTINCT in SELECT COUNT(DISTINCT foo) FROM bar do anything.
回答5:
Works for me. I get 3 rows back.
$ perl x.pl
'Oberhemd'
'Mantel'
'Hose'
3 rows
perl -MDBI -le 'DBI->installed_versions;'
Perl : 5.010001 (i686-linux-gnu-thread-multi)
OS : linux (2.6.24-28-server)
DBI : 1.617
DBD::mysql : 4.020
DBD::Sys : 0.102
DBD::Sponge : 12.010002
DBD::SQLite : 1.33
DBD::Proxy : 0.2004
DBD::Pg : 2.17.2
DBD::Oracle : 1.38
DBD::ODBC : 1.33
DBD::Multiplex : 2.014122
DBD::Gofer : 0.015057
DBD::File : 0.40
DBD::ExampleP : 12.014310
DBD::DBM : 0.06
DBD::CSV : 0.30
Added:
perl -MSQL::Statement -le 'print $SQL::Statement::VERSION'
1.31
Version 1.23, release November 20th, 2009 * Correct handling of DISTINCT in aggregate functions
回答6:
I met the same problem.
You can turn around this problem using a GROUP BY statement instead of DISTINCT.
This is just a turn around waiting for the resolution of a bug ...
来源：https://stackoverflow.com/questions/1941321/does-select-distinct-work-with-perls-dbdcsv