Perl 数据查询的技术
今天测试查询数据的时候发现一个很奇异的问题,对着这个问题做了个研究。
先看代码,具体如下:
#!/usr/bin/perl use TDmodule; # create object $test=TDmodule->new(); # connect db return config $config=$test->connect_db("3d_database","localhost","root","mojige123"); # select for db return database $old=$test->select_db($config,"select * from old_papar"); $user=$test->select_db($config,"select * from user_papar"); sub result{ local($sql)=shift; local($task)=shift; # print execute result while($list=$sql->fetchrow_hashref()){ push(@target,$list->{$task}); } return @target; } @old_papar=result($old,'id'); @user_papar=result($user,'number'); foreach my $a (@old_papar){ print "$a\n"; } print "--------------\n"; foreach my $b (@user_papar){ print "$b\n"; }
在这种情况下读出的数据会有重复读取的问题,例如目标数据要求是每个表读取一次,但是这个方法看起来是读取一次,实际上是读取了两次。具体结果如下所示:
root@crunchbang:~# perl TDmodule.pl 1 2 3 4 5 6 7 8 9 10 11 -------------- 1 2 3 4 5 6 7 8 9 10 11 145 404 693 6 168 18 746 429 206 403 319
第一次的结果将会包含到第二次中,为了解决这个问题,我仔细的修改了下代码,发现,只需要每次将容器清空,即可。在此MARK一下。方便以后查询。
#!/usr/bin/perl use TDmodule; # create object $test=TDmodule->new(); # connect db return config $config=$test->connect_db("3d_database","localhost","root","mojige123"); # select for db return database $old=$test->select_db($config,"select * from old_papar"); $user=$test->select_db($config,"select * from user_papar"); sub result{ local($sql)=shift; local($task)=shift; # clean list array @target=(); # print execute result while($list=$sql->fetchrow_hashref()){ push(@target,$list->{$task}); } return @target; } @old_papar=result($old,'id'); @user_papar=result($user,'number'); foreach my $a (@old_papar){ print "$a\n"; } print "--------------\n"; foreach my $b (@user_papar){ print "$b\n"; }