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Question

我编写了一个使用连接和子查询的MySQL查询，最后在最外面的SELECT语句中获取了所需的列。它类似于：

SELECT X,Y,Z
FROM
(SELECT A,B,C,X 
FROM T1 
JOIN
(SELECT D,E,F,Y
FROM T2) ALIAS ON CONDITION....

依此类推。现在，我想做Z/Y，所以我做了

SELECT X,Y,Z,Z/Y
FROM
YADA YADA YADA

这适用于MySQL，但是当我在Java程序中做同样的事情时，它会抛出一个错误，说：

You have an error in your SQL syntax; check the manual that corresponds to your 
MySQL server version for the right syntax to use near 'Z/Y'

我如何克服这个问题？

Answer 1

事实证明，我忘记在倒数第二列添加一个逗号，这导致了问题。感觉就像一个doofus！

Answer 2

是的，你是。我也是。在光明的一面，至少我要在我的oracle帐户上重置密码。

import java.sql.*;

public class TwoAndTwo {
  private Connection connect = null;
  private Statement statement = null;
  private PreparedStatement preparedStatement = null;
  private ResultSet resultSet = null;

  public void readDataBase() throws Exception {
    try {
      Class.forName("com.mysql.jdbc.Driver");
      connect = DriverManager
          .getConnection("jdbc:mysql://localhost/foobar?"
              + "user=root&password=root");

      statement = connect.createStatement();
      resultSet = statement
          .executeQuery("select 2+2 as computation");

      resultSet.next();
      System.out.println( resultSet.getString("computation"));
    } catch (Exception e) { throw e; } finally { close(); }
  }
  private void close() {
    try { if (resultSet != null) { resultSet.close(); }
      if (statement != null) { statement.close(); }
      if (connect != null) { connect.close(); }
    } catch (Exception e) {
      e.printStackTrace(); }
  }
  public static void main(String[] argv) {
      TwoAndTwo tnt = new TwoAndTwo();
      try { tnt.readDataBase();
      } catch (Exception e) {
          System.out.println(e.getMessage());
          e.printStackTrace();
      }
  }
}

输出

$ javac TwoAndTwo.java 

$ java -cp mysql-connector-java-5.1.29-bin.jar:.  TwoAndTwo 
4

使用JDBC / MySQL在SELECT语句中的Math Expression

2 个答案:

输出