无论如何在同一个SELECT子句中使用列别名？例如:
SELECT ord_id, candy_id, price, quantity,
price * quantity AS ext_cost, ext_cost * @tax_rate
返回错误,因为MySQL ext_cost在ext_cost * @tax_rate查询中无法识别" " .如果不可能,可以返回一个包含第一个查询中列出的所有内容的表,而不必写这样的内容吗？
SELECT ord_id, candy_id, price, quantity,
price * quantity AS ext_cost, (price * quantity) * @tax_rate
基本上,我只是想知道无论如何都要ext_cost在SELECT查询中重用.
试图让这个工作,但我遇到了麻烦.我按照以下说明操作:https: //www.railstutorial.org/book/beginning#cha-beginning
我到达1.3.2然后输入:
rails server -b $IP -p $PORT
这导致此错误而不是WEBrick运行:
/usr/local/rvm/gems/ruby-2.1.5@rails4/gems/sass-rails-5.0.1/lib/sass/rails/helpers.rb:11:in `<top (required)>': uninitialized constant Sass::Script (NameError)
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/sass-rails-5.0.1/lib/sass/rails.rb:8:in `require'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/sass-rails-5.0.1/lib/sass/rails.rb:8:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/sass-rails-5.0.1/lib/sass-rails.rb:1:in `require'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/sass-rails-5.0.1/lib/sass-rails.rb:1:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:76:in `require'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:76:in `block (2 levels) in require'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:72:in `each'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:72:in `block in require'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:61:in `each'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler/runtime.rb:61:in `require'
from /usr/local/rvm/gems/ruby-2.1.5@global/gems/bundler-1.7.6/lib/bundler.rb:133:in `require'
from /home/ubuntu/workspace/hello_app/config/application.rb:7:in `<top (required)>'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:78:in `require'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:78:in `block in server'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `tap'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:75:in `server'
from /usr/local/rvm/gems/ruby-2.1.5@rails4/gems/railties-4.2.0/lib/rails/commands/commands_tasks.rb:39:in …我将如何在MySQL中编写声明以返回上一季度的上一个开始和结束日期？如果我想要在此之前的季度的开始和结束日期(即去年十月的开始和去年十二月底),请说.