java mysql 计算行数

Question

我创建此代码是为了计算表格中的行数。但是，我无法返回计数，并显示错误“无法从结果类型为 void 的方法返回值”。有人可以告诉我我的错误在哪里吗？非常感谢!

public void num() throws Exception {
  try {
      // This will load the MySQL driver, each DB has its own driver
      Class.forName("com.mysql.jdbc.Driver");
      // Setup the connection with the DB
      connect = DriverManager.getConnection("jdbc:mysql://localhost/testdb?"
      + "user=root&password=");

      // Statements allow to issue SQL queries to the database
      statement = connect.createStatement();
      resultSet = statement.executeQuery("select * from testdb.emg");
      int count = 0;
      while (resultSet.next()) {
        count++;
      }  
      return count;
  } catch (Exception e) {
  }

Answer 1

试试下面的代码

 public int num() throws Exception {
 try {
 // This will load the MySQL driver, each DB has its own driver
 Class.forName("com.mysql.jdbc.Driver");
 // Setup the connection with the DB
 connect = DriverManager.getConnection("jdbc:mysql://localhost/testdb?"
 + "user=root&password=");

 // Statements allow to issue SQL queries to the database
 statement = connect.createStatement();
 resultSet = statement.executeQuery("select count(*) from testdb.emg");

 while (resultSet.next()) {
 return resultSet.getInt(1);
 }
} catch (Exception e) {
}

下面是错误

1. public void num() 抛出异常 {

   应该是

   public int num() 抛出异常 {

2. 要计算总行数，您应该使用查询 select count(*) from testdb.emg

如果有任何问题，请告诉我。