带有WHERE的Oracle JDBC select返回0 [英] Oracle JDBC select with WHERE return 0

问题描述

类似的问题: JDBC的奇怪问题，select返回null 但是人们并没有要求.

Similar question to: Strange problem with JDBC, select returns null but people didn't ask for this.

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.我尝试在执行之前记录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查询返回表中所有行的编号. 我将Oracle 10g与ojdbc-14.jar(来自Maven Repo的最新版本)和Java 6配合使用.

This code always return 0. I try to log sql before execution and try to run it in SQLdeveloper and get correct value (over 100). When I remove WHERE, sql = "Select count(*) from MyTable query return number of all rows in table. I use Oracle 10g with ojdbc-14.jar (last version from maven repo) and Java 6.

推荐答案

day的引用不正确，我建议使用一条准备好的语句 like 一条准备好的语句，如下所示:

day has not been quoted correctly, I would suggest using a prepared statement like a prepared statement as follows:

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

与以下相同:

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

与后者相比有几个优点(主要是安全性和性能).参见:

with several advantages over the latter (mainly security and performance). See:

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

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