Java 示例 - 使用列方法

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  问题描述

  如何使用不同的列方法来计算列数、获取列名、获取列类型等？
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  解决方案

  以下示例使用 getColumnCount、getColumnName、getColumnTypeName、getColumnDisplaySize 方法获取表中的列数、列名或列类型。

  
  import java.sql.*;
  public class jdbcConn {
     public static void main(String[] args) throws Exception {
        Class.forName("org.apache.derby.jdbc.ClientDriver");
        Connection con = DriverManager.getConnection(
           "jdbc:derby://localhost:1527/testDb","name","pass");
        
        Statement stmt = con.createStatement();
        String query = "select * from emp order by name";
        
        ResultSet rs = stmt.executeQuery(query);
        ResultSetMetaData rsmd = rs.getMetaData();
        
        System.out.println("no of columns in the table = "+ rsmd.getColumnCount());
        System.out.println("Name of the first column "+ rsmd.getColumnName(1));
        System.out.println("Type of the second column "+ rsmd.getColumnTypeName(2));
        System.out.println("No of characters in 3rd column "+ rsmd.getColumnDisplaySize(2));
     }
  }
  

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  结果

  上面的代码示例将产生以下结果。结果可能会有所不同。

  
  no of columns in the table = 3
  Name of the first columnID
  Type of the second columnVARCHAR
  No of characters in 3rd column20
  

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