Question

类似的问题： Strange problem with JDBC, select returns null 但人们没有要求这样做。

我的代码：

public int myMethod(String day) throws SQLException{
  String sql = "Select count(*) from MyTable WHERE someColumn = " + day;
  Connection connection = ConnFactory.get();
  PreparedStatement prepareStatement = null;
  ResultSet resultSet = null;
  int ret = -1;
  try{
      prepareStatement = connection.prepareStatement(sql);
      resultSet = prepareStatement.executeQuery(sql);
      if(resultSet.next()){
          ret = resultSet.getInt(1);
      }
  }
  catch(SQLException sqle){
      // closing statement & ResultSet, log and throw exception
  }
  finally{
     // closing statement & ResultSet
  }
  ConnFactory.kill(connection);

  return ret;
}

此代码始终返回0.我尝试在执行前记录sql并尝试在SQLdeveloper中运行它并获得正确的值（超过100）。当我删除WHERE时，sql = "Select count(*) from MyTable查询表中所有行的返回数。我使用Oracle 10g和ojdbc-14.jar（来自maven repo的最新版本）和Java 6。

Answer 1

day未被正确引用，我建议使用预备语句，如准备好的声明，如下所示：

...
try {
    prepareStatement = connection.prepareStatement("Select count(*) from MyTable WHERE someColumn = ?");
    prepareStatement.setString(1,day);
...

与：

相同

sql = "Select count(*) from MyTable WHERE someColumn = '" + day + "'";

具有优于后者的几个优点（主要是安全性和性能）。参见：

http://java.sun.com/docs/books/tutorial/jdbc/basics/prepared.html

Answer 2

首先使用这样的sql是不可取的。因为它会导致SQL注入。

将来尝试使用如下所示并使用PreparedStatement执行

String sql = "Select count(*) from MyTable WHERE someColumn = ? "

您的解决方案是否尝试

String sql = "Select count(*) from MyTable WHERE someColumn = '" + day + "'";

Answer 3

karim79是个很好的答案，你忘了在你的“日期”值中添加撇号标记

String sql = "Select count(*) from MyTable WHERE someColumn = '" + day + "'";

Oracle JDBC选择WHERE返回0

3 个答案: