Checking if email id already exists in database using JSP

Question

I want that a particular email id shouldn't be used more than once when doing registration. Here's my code:

if(request.getParameter("btn1")!=null)
  {
      String unm=request.getParameter("nm");
      String em=request.getParameter("email");
      String pwd=request.getParameter("pass");
      Connect c1=new Connect();
       String q="insert into register(name,email,password) values('"+unm+"','"+em+"','"+pwd+"');";
    int rs=c1.DMLExecuter(q);
    if(rs>0)
    %>
    <script>
        alert("You are registered now. Please login to continue.");
    </script>

What should I do to check if the email id is being used twice?

Answer 1

1. ensure that your email field is unique, such as by adapting the DDL accordingly (this will get the database to ensure that e-mail addresses are unique). Alternatively, the e-mail field could be made primary key:

    CREATE TABLE register( ... EMAIL VARCHAR(50) NOT NULL UNIQUE, ... ) 

2. In the code, before inserting, check the count of existing e-mails by that ID:

    long existingCount = ... String countQuery = "SELECT COUNT(1) FROM register WHERE email = ?" 

Run this query with the value of request.getParameter("email") . The result should be a number telling you the number of existing users with that e-mail.

Assuming that count has been stored in the existingCount variable:

if(existingCount == 0) {
    //Put here the code to insert the new user as shown in your question...
} else {
%>
    <script>
        alert("You are already registered. Login or choose a different email");
    </script>
<%
}

Note that my sql used bind variables , please use a prepared statement