如何编写条件sql查询？

Question

我有一张叫做学生的表：

name age roll_no



X    Y

我想写一个sql查询，如果name =＆＃39; X＆＃39;和年龄=＆＃39; Y＆＃39;然后插入＆＃39; Z＆＃39; to roll_no。 我怎么能这样做？

Answer 1

没有插入而是更新。

root 'sessions#login'
  get 'homes/home'
  get '/login' => "sessions#login", :as => "login"
  get '/logout' => "sessions#logout", :as => "logout"
  get '/homes' => "homes#home"
  resources :users
  resources :sessions
  resources :homes
  resources :teachers
  resources :teacher_details
  resources :profiles