JDBC MySQL 多表关联查询查询

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public static void main(String[] args) throws Exception{ Class.forName("com.mysql.jdbc.Driver"); Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/mydb","root",""); String sql ="select * from info"; 　　　　　//关联查询时,可以直接join on.但是效率不高 　　　　　//String sql ="select info.Code,info.Name,info.Sex,nation.Name sb ,info.Birthday from info join nation on info.Nation=nation.Code "; 　　　　　 Statement state = conn.createStatement(); ResultSet rs = state.executeQuery(sql); while(rs.next()){//判断是否还有下一行　　　　　　　　　　 System.out.print(rs.getString(1)+"\t"); System.out.print(rs.getString(2)+"\t"); System.out.print(rs.getBoolean(3)?"男\t":"女\t"); //?:简单判断 System.out.print(minzu(rs.getString(4))+"\t"); System.out.println(bianhuan(rs.getDate(5))); } conn.close(); } //关联查询时,也能写个方法再查一遍另一个表，然后赋给原来的列 private static String minzu(String m)throws Exception { String mz= "";//定义空字符串 Class.forName("com.mysql.jdbc.Driver"); Connection conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/mydb","root",""); Statement sta = conn.createStatement(); String sql = "select * from nation where code = '"+m+"'"; ResultSet rs = sta.executeQuery(sql); if(rs.next() == true){　//有对应的sql语句的时候，才执行 mz = rs.getString(2);//另一个表的的列赋值给mz } conn.close(); return mz; //返回mz } //日期时间转换 public static String bianhuan(Date d){ SimpleDateFormat f = new SimpleDateFormat("yyyy年mm月dd日"); return f.format(d); }

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