sql简单测试

本文介绍了SQL的基本操作,包括数据查询、更新、删除和插入等核心功能,并提供了具体示例,如条件筛选、排序及计数等。

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SQL简单测试:

  1. SQL指的是Structured Query Language
  2. 从数据库中提取数据:SELECT
  3. 更新数据库中的数据:UPDATE
  4. 删除数据库中的数据:DELETE
  5. 在数据库中插入新的数据:INSERT INTO
  6. 从“Persons”表中选取“FirstName”列:SELECT FirstName FROM Persons
  7. 从"Persons"表中选取所有的列:SELECT * FROM Persons
  8. 从“Persons”表中选取“FirstName”列的值等于“Peter”的所有记录:SELECT * FORM Persons WHERE FirstName="Peter"
  9. 从“Persons”表中选取“FirstName”列的值以“a”开头的所有记录:SELECT * FROM Persons WHERE FirstName LIKE 'a%'
  10. 当所列出的某个条件为 true 时,OR 运算符会显示记录。当列出的所有条件为 true 时,AND 运算符会显示记录。
  11. 如何在表 Persons 中选择 FirstName 等于 Thomas 而 LastName 等于 Carter 的所有记录:SELECT FORM Persons WHERE FirstName='Thomas' AND LastName='Carter'
  12. 如何按字母顺序选取 Persons 表中 LastName 介于 Adams 和 Carter 的所有记录:SELECT FROM Persons WHERE LastName BETWEEN 'Adams' AND 'Carter'
  13. 返回唯一不同的值:SELECT DISTINCT

    哪条SQL 语句可返回唯一不同的值

    A.
    UNIQUE是完整性约束里的一种,如果某列的值需要是唯一的那么就添加UNIQUE约束
    Distinct是在查询时用的,若在SELECT的列选择列表中的某列说明为Distinct,那么查询出来的结果里,该列不会出现重复的值.

    B.
    unique是distinct的同义词,功能完全相同。
    distinct是标准语法,其他数据库 sql server,db2,oracle,sybase,mysql等都支持。unique,informix数据库认识,其他数据库有的认识,有的不认识。

    C.
    用UNIQUE和DISTINCT查找不重复的行,语法好像是一样的,结果也是一样的,他们究竟有什么区别?别人的回答是:一样的。总之,效果是一样的,但是还是按照习惯和规章来吧。select 就用distinct。

  14. 对结果集进行排序:ORDER BY
  15. 如何根据 "FirstName" 列降序地从 "Persons" 表返回所有记录:SELECT * FROM Persons ORDER BY FirstName DESC
  16. 向“Persons”表插入新的记录:INSERT INTO Persons VALUES ('Tom','Rose')
  17. 向 "Persons" 表中的 "LastName" 列插入 "Wilson":INSERT INTO Persons (LastName) VALUES ('Wilson')
  18. 把 "Persons" 表中 "LastName" 列的 "Gates" 改为 "Wilson":UPDATE Persons SET  LastName='Wilson' WHERE LastName='Gates'
  19. 在 "Persons" 表中删除 "FirstName" 等于 "Fred" 的纪录:DELETE FROM Persons WHERE FirstName='Fred'
  20. 返回"Persons"表中的数目:SELECT COUNT(*) FROM Persons

转载于:https://www.cnblogs.com/Try-kevin/p/7905180.html

package com.bjsxt.servlet; import com.bjsxt.entity.User; import com.bjsxt.service.UserService; import com.bjsxt.service.impl.UserServiceImpl; import javax.servlet.RequestDispatcher; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.*; import java.io.IOException; import java.net.URLEncoder; import java.sql.Date; import java.util.ArrayList; import java.util.Arrays; import java.util.List; public class UserServlet extends BaseServlet { // @Override // protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // //解决POST单的中文乱码问题 // request.setCharacterEncoding("utf-8"); // //接收method属性的值 // String methodName = request.getParameter("method"); // // //根据method属性的值调用相应的方法 // if("login".equals(methodName)){ // this.login(request,response); // }else if("register".equals(methodName)){ // this.register(request,response); // }else if("logout".equals(methodName)){ // this.logout(request,response); // } // // } public void show(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取单的数据 String userId = request.getParameter("userId"); if(userId == null){ userId = ""; } String strAge = request.getParameter("minAge"); int minAge = 0; try{ minAge = Integer.parseInt(strAge); //"12" "abc" }catch(NumberFormatException e){ e.printStackTrace(); } //调用业务层完成查询操作 UserService userService = new UserServiceImpl(); //List<User> userList = userService.findAll(); List<User> userList = userService.find(userId,minAge); //List<User> userList = null; //List<User> userList = new ArrayList<User>(); //跳转到show.jsp显示数据 request.setAttribute("userId",userId); request.setAttribute("minAge",strAge); request.setAttribute("ulist",userList); request.getRequestDispatcher("/admin/show.jsp").forward(request,response); } public void logout(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //结束当前的session request.getSession().invalidate(); //跳转回登录页面 response.sendRedirect(request.getContextPath()+"/admin/login.jsp"); } public void register(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //request.setCharacterEncoding("utf-8"); //1.接收来自视图层的单数据 String userId = request.getParameter("userId"); String realName = request.getParameter("realName"); String pwd = request.getParameter("pwd"); String rePwd = request.getParameter("repwd"); int age = Integer.parseInt(request.getParameter("age"));// "23" String [] hobbyArr = request.getParameterValues("hobby"); String strDate = request.getParameter("enterDate");//"1999-12-23" Date enterDate = Date.valueOf(strDate); //util.Date SimpleDateFormat //判断两次密码是否相同 if(pwd == null || !pwd.equals(rePwd)){ request.setAttribute("error","两次密码必须相同"); request.getRequestDispatcher("/admin/register.jsp").forward(request,response); return; } //2.调用业务层完成注册操作并返回结果 User user = new User(userId,realName,pwd,age, Arrays.toString(hobbyArr),enterDate); UserService userService = new UserServiceImpl(); int n = userService.register(user); //3.根据结果进行页面跳转 if(n>0){ response.sendRedirect(request.getContextPath()+"/admin/login.jsp"); }else{ request.setAttribute("error","注册失败"); request.getRequestDispatcher("/admin/register.jsp").forward(request,response); } } public void login(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //解决POST单的中文乱码问题 //request.setCharacterEncoding("utf-8"); //获取用户名和密码 request 内建对象 请求 String username = request.getParameter("username"); String password = request.getParameter("password"); String rememberme = request.getParameter("rememberme"); //调用下一层判断登录是否成功,并返回结果 //进行服务器端的单验证 if(username ==null || "".equals(username)){ request.setAttribute("error","用户名不能为空JSP"); request.getRequestDispatcher("/admin/login.jsp").forward(request,response); return; } if (username.length()<=6){ request.setAttribute("error","用户名长度必须大于6JSP"); request.getRequestDispatcher("/admin/login.jsp").forward(request,response);//后面语句还会执行 return; //后面的语句不再执行 } // boolean flag = false;//默认失败 // if(username.indexOf("sxt")>=0 || username.contains("尚学堂")){ // flag = true; // } User user = null;//默认登录失败 // UserDao userDao = new UserDaoImpl(); // user = userDao.find(username,password); UserService userService = new UserServiceImpl(); user = userService.login(username,password); //userService.addOrder("shoppingCart"); //输出结果 if(user != null){ //登录成功才记住我 //1.办理会员卡 String username2 = URLEncoder.encode(username,"utf-8"); Cookie cookie1 = new Cookie("uname",username2); Cookie cookie2 = new Cookie("password",password); //2.指定会员卡的作用范围,默认范围是当前目录 /servlet/LoginServlet /admin/login.jsp //cookie1.setPath("/"); //当前服务器 cookie1.setPath("/myservlet2/"); //当前项目 cookie2.setPath("/myservlet2"); //3.指定会员卡的作用时间 if("yes".equals(rememberme)){ cookie1.setMaxAge(60*60*24*10); //默认的时间浏览器不关闭的时间;-1 示一直有效 cookie2.setMaxAge(60*60*24*10); }else{ cookie1.setMaxAge(0); cookie2.setMaxAge(0); } //4.将会员卡带回家 response.addCookie(cookie1); response.addCookie(cookie2); //成功跳转到成功页面 //out.println("登录成功"); // /servlet/LoginServlet // /servlet/success.jsp // request.getRequestDispatcher("/admin/success.jsp").forward(request,response); HttpSession session = request.getSession(); // session.setAttribute("username",username); session.setAttribute("user",user); //response.sendRedirect("/myservlet2/admin/success.jsp"); //response.sendRedirect("https://www.bjsxt.com:443/news/11377.html"); //response.sendRedirect("http://localhost:8080/myservlet2/admin/success.jsp"); //response.sendRedirect("/myservlet2/admin/success.jsp"); //response.sendRedirect("/myservlet2/admin/success.jsp"); //response.sendRedirect(request.getContextPath()+"/admin/success.jsp"); //http://192.168.58.250:8080/myservlet2/servlet/LoginServlet //http://192.168.58.250:8080/myservlet2/admin/success.jsp //登录成功后,网站的访问人数+1 //1.获取当前的访问人数 ServletContext context = this.getServletContext(); Integer count2 = (Integer) context.getAttribute("count"); //2.人数+1 if(count2 == null){ //第一个用户 count2 = 1; }else{ count2++; } //3.再存放到application作用域中 context.setAttribute("count",count2); //http://192.168.58.250:8080/myservlet2/servlet/admin/success.jsp response.sendRedirect("../admin/success.jsp"); }else{ //失败跳转回登录页面 //out.println("登录失败"); request.setAttribute("error","用户名或者密码错误"); // RequestDispatcher rd = request.getRequestDispatcher("/admin/login.jsp"); // rd.forward(request,response); //RequestDispatcher rd = request.getRequestDispatcher("http://localhost:8080/myservlet2/admin/login.jsp"); //RequestDispatcher rd = request.getRequestDispatcher("/admin/login.jsp"); //http://192.168.58.250:8080/myservlet2/servlet/admin/login.jsp RequestDispatcher rd = request.getRequestDispatcher("../admin/login.jsp"); rd.forward(request,response); } } }
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