如何找到列mysql的最大值并返回值？

Question

我想搜索列的最大值,但找到的值始终为0

public  int maXnumR()
{
    DataBase s = DataBase.getInstance();
    int numR= getnumR();

    String req1 = "SELECT max(`idrf`) FROM   `reference`  WHERE `numR` = "
        + numR + " GROUP BY `numR` ";

    try 
    {
        Statement m=  s.getConn().createStatement();
        ResultSet r1 = m.executeQuery(req1);
        while (r1.next()) 
        {
            maxnumR =r1.getInt("idrf");
            nbp++;  
        } 
    } 
    catch (SQLException e1) 
    {
        e1.printStackTrace();
        System.out.println("maXnumR : "+e1);
    } 
    return maxnumR;
}

maXnumR返回0并且表不为空.

如果我执行查询它可以正常使用MySQL

ERREUR:

java.sql.SQLException: Column 'idrf' not found.
maXnumR : java.sql.SQLException: Column 'idrf' not found.
idrf existe:0

Answer 1

尝试

SELECT max(`idrf`) as idrf