用几个表实现 JOIN

Question

我有这张表，我想从中选择许多行并使用 JOIN 将两个表中的 id 转换为 name。我试过这个：

主表：

@Entity
@Table(name = "payment_transactions")
public class PaymentTransactions implements Serializable {
    ..... 
    @Column(length = 4)
    private Integer merchant_id;

    @Column(length = 4)
    private Integer terminal_id; 
    ......
}

带有附加数据的表格：

@Entity
@Table(name = "merchants")
public class Merchants implements Serializable {

    @Column(name = "id")
    private int id;

    @Column(length = 255)
    private String name;
    .........
}


@Entity
@Table(name = "terminals")
public class Terminals implements Serializable {

    @Column(name = "id")
    private int id;

    @Column(length = 255)
    private String name;
    .........
}

我试过了：

String hql = "select e.* from " + PaymentTransactions.class.getName() + " e "
                + " INNER JOIN " + Merchants.class.getName() + " m "
                + " ON e.id = m.merchant_id AND " 
                + " INNER JOIN " + Terminals.class.getName() + " t "
                + " ON e.id = t.terminal_id "
                + " where e.created_at >= :start_date and e.created_at <= :end_date";

一般的想法是我想要一个主表Payment transactions，它将merchant_id 和terminal_id 存储为数字。通过加入，我想获得商家和终端的名称。实现这一点的正确方法是什么？

Answer 1

您只需将这些变量添加到查询中的列列表中：

String hql = "select e.*, m.name AS merchant, t.name AS terminal"
                + " FROM " + PaymentTransactions.class.getName() + " e "
                + " INNER JOIN " + Merchants.class.getName() + " m "
                + " ON e.id = m.merchant_id AND " 
                + " INNER JOIN " + Terminals.class.getName() + " t "
                + " ON e.id = t.terminal_id "
                + " where e.created_at >= :start_date and e.created_at <= :end_date";

请注意，您需要添加列别名以避免在输出结果中出现两次相同的列名 (name)。查询包括这些（例如m.name AS merchant），因此您可以在获取结果时以merchant 列的形式访问商家名称。