从db2获取Resultset

Question

import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.DriverManager;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.SQLException;
import java.sql.Statement;

public class Db2{
    public static void main(String[] argv) {
        try {
            Class.forName("com.ibm.db2.jcc.DB2Driver");
        }
        catch (ClassNotFoundException e) {
            System.out.println("Please include Classpath  Where your DB2 Driver is located");
            e.printStackTrace();
            return;
        }
        System.out.println("DB2 driver is loaded successfully");
        Connection conn = null;
        PreparedStatement pstmt = null;
        ResultSet rs=null;
        Statement stmt = null;
        boolean found=false;
        String name = "";
        try {
            conn = DriverManager.getConnection("jdbc:db2://server:900/MyDB"
                    +":user=user1;password=swim;"+
                     "traceLevel=" +
                     (com.ibm.db2.jcc.DB2BaseDataSource.TRACE_ALL) + ";");
            if (conn != null)
            {
                System.out.println("DB2 Database Connected");
            }
            else
            {
                System.out.println("Db2 connection Failed ");
            }

            // Create the Statement
            stmt = conn.createStatement();                                            
            System.out.println("**** Created JDBC Statement object");

            // Execute a query and generate a ResultSet instance
            rs = stmt.executeQuery("SELECT * FROM VIRTUALMACHINE");                    
            System.out.println("**** Created JDBC ResultSet object");

            device
            while (rs.next()) {
              name = rs.getString(2);
              System.out.println("Name = " + name);
            }
            System.out.println("**** Fetched all rows from JDBC ResultSet");
            // Close the ResultSet
            rs.close();
            System.out.println("**** Closed JDBC ResultSet");



        } catch (SQLException e) {
            System.out.println("DB2 Database connection Failed");
            e.printStackTrace();
            return;
        }
    }

}

我想知道为什么当我运行它时它不返回任何东西。当我将查询字符串从select VIRTUALMACHINE from mydb更改为“select*from syscat.columns WHERE tabschema='gga'AND tabname='VIRTUALMACHINE'fetch first 10 rows only”时，我得到一个结果。在这种情况下

DB2驱动程序成功加载DB2数据库连接****创建JDBC语句对象****创建JDBC ResultSet对象名称=GGA名称=GGA名称=GGA名称=GGA
****从JDBC ResultSet提取所有行****关闭JDBC ResultSet

这差不多是对列的描述。我想知道为什么select VIRTUALMACHINE from mydb没有产生任何结果。这不是DB2中查询的方式吗？

Answer 1

当对象不存在时抛出SQLSTATE 42704。

from子句引用的是表名，而不是DB。表名可以是合格的，也可以是不合格的；并且从技术上讲,限定表名可以包括远程DB名。

你说这个行得通：

SELECT * 
FROM SYSCAT.COLUMNS 
WHERE TABSCHEMA= 'GGA' AND TABNAME= 'VIRTUALMACHINE' 
fetch first 10 rows only

select *
from GGA.VIRTUALMACHINE