java mysql count行数 [英] java mysql count number of rows

问题描述

我创建了这段代码，允许我计算表格中的行数。但是，我无法返回计数的数字，并显示无法从结果类型为void的方法返回值。有人能告诉我'我的错误在哪里？非常感谢！

I created this code to allow me calculate the number of rows in my table. However, I'm not able to return the counted number with an error saying "cannot return a value from method whose result type is void." Could someone show me where' my error? Thanks alot!

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) {
  }

推荐答案

尝试以下代码

 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) {
}

以下是错误

1. public void num（）抛出异常{

应该是

public int num（）抛出异常{

要计算总行数，您应该使用查询从testdb.emg中选择count（*）

For counting total rows you should use query select count(*) from testdb.emg

让我知道任何问题。

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