sql - 列名包含下划线时的语法错误

Question

我可以编译但不能执行下面的代码出现错误(使用 Postgres):

Fatal database error
ERROR: syntax error at or near "as"
Position: 13

---

import java.sql.*;
public class JDBCExample
{
private static final String JDBC_DRIVER = "org.postgresql.Driver";
private static final String URL = "jdbc:postgresql://hostname/database";
private static final String USERNAME = "username";
private static final String PASSWORD = "password";

public static void main(String[] args) throws Exception
{
  Connection dbConn = null;
  Statement query = null;
  ResultSet results = null;

  Class.forName(JDBC_DRIVER);

  try
  {
     dbConn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
  }
  catch (SQLException e)
  {
     System.out.println("Unable to connect to database\n"+e.getMessage());
     System.exit(1);
  }

  try
  {
     query = dbConn.createStatement();
     results = query.executeQuery("select 20_5 as name from flowshop_optimums");

    while (results.next())
    {
      System.out.println(results.getString("name"));
    }

    dbConn.close();
  }
  catch (SQLException e)
  {
     System.out.println("Fatal database error\n"+e.getMessage());
     try
     {
        dbConn.close();
     }
     catch (SQLException x) {}
     System.exit(1);
  }

} // main

} // Example

Answer 1

这不是下划线，而是列名以数字开头的事实。你需要逃避这个。

对于 MySQL，使用反引号。

select `20_5` as name from flowshop_optimums

对于 SQL Server，使用方括号。

select [20_5] as name from flowshop_optimums

对于 PostgreSQL，使用双引号。

select "20_5" as name from flowshop_optimums