java - 无法使用 JDBC 连接获取计数

Question

我无法通过查询来获取行数。我已经使用了 JDBC 连接。但是，它没有显示任何错误，但它停止执行该过程。

这是我的代码

Transaction transaction=null;
    Connection c = null;
    Statement stmt = null;
    ResultSet result;
    try {
         Class.forName("org.postgresql.Driver");
         c = DriverManager.getConnection(
         "jdbc:postgresql://192.168.1.7:5432/"+userDB,
     "postgres", "openerp");
     } catch (Exception e) {
         e.printStackTrace();
         System.err.println(e.getClass().getName() + ": " + e.getMessage());
         System.exit(0);
     }
    int count = 0;
    try {   
        LOGGER.info("In try of get");
        factory = HibernateUtil.connectDB(userDB);
        LOGGER.info("Connected to DB");
        //Open Session
        session = factory.openSession();
        //Begin Transaction
        transaction = session.beginTransaction();
        LOGGER.info("Beginning the transaction");
        stmt = c.createStatement();
        String sql = "SELECT COUNT(*) FROM mycontent_messages where status = '0'";

        count = stmt.executeUpdate(sql);
        LOGGER.info("successfully got count : "+count);
        c.commit();
        stmt.close();
        c.close();   

我得到的异常是

org.postgresql.util.PSQLException: A result was returned when none was expected.
at    org.postgresql.jdbc2.AbstractJdbc2Statement.executeUpdate(AbstractJdbc2Statement.java:307)
at net.vsspl.mycontent.daoimpl.contentImpl.getUnreadCount(contentImpl.java:379)
at net.vsspl.mycontent.services.countUnreadMessages.main(countUnreadMessages.java:49)

它记录到“开始交易”。之后就没有显示任何东西了。我的代码有问题吗？

Answer 1

您想要从查询中获取结果集并以这种方式处理它，而不是获取受影响的行数..

ResultSet rs =  stmt.executeQuery(sql);
 int count = 0;
 if(rs.next())
 {
    count = rs.getInt(1);
  }