摘要： #！/usr/bin/perlsub total { my $sum; foreach (@_) { $sum += $_; }}sub average { if (@_ == 0 ) { return } my $sum = total(@_); my $count = @_; $sum/$count;}sub above_average { my $average = average(@_); my @list; foreach $element (@_) { if ($element > $average) { push @list,$element; } }@list;}my @ 阅读全文

摘要： 1.内联结(等值联结)select vend_name,prod_name,prod_pricefrom vendors,productswhere vendors.vend_id = products.vend_id等效于select vend_name,prod_name,prod_pricefrom vendors inner join productson vendors.vend_id = products.vend_id2.左联结select customers.cust_id,orders.order_numfrom customers left outer join order 阅读全文