Question

我想知道如何使用内部连接器以其他方式选择一列两次。我的数据库是sqlite，我使用的是PDO db驱动程序。

我的例子：

    SELECT
            orders.id,
            orders.order_number,
            clients.first_name,
            clients.last_name,
            users.name AS user_name
    FROM orders

    INNER JOIN clients ON
            orders.client_id = clients.id

    INNER JOIN users ON
            orders.created_by = users.id

我还想得到编辑此记录的user_name

            orders.edited_by = users.id

如何加入此选择？

Answer 1

您需要使用表别名。

SELECT
        orders.id,
        orders.order_number,
        clients.first_name,
        clients.last_name,
        creator.name AS creator_user_name
        editor.name AS editor_user_name
FROM orders

INNER JOIN clients ON
        orders.client_id = clients.id

INNER JOIN users creator ON
        orders.created_by = creator.id

INNER JOIN users editor ON
        orders.edited_by = editor.id

Answer 2

在表名中使用aliases，这样就可以对同一个表使用多个引用。这也有助于使大型查询更易于阅读。

SELECT
        orders.id,
        orders.order_number,
        clients.first_name,
        clients.last_name,
        createUsers.name AS creator_name,
        editUsers.name AS editor_name
FROM orders

INNER JOIN clients ON
        orders.client_id = clients.id

INNER JOIN users As createUsers ON
        orders.created_by = users.id

INNER JOIN users As editUsers ON
        orders.edited_by = users.id

您可以根据需要使用同一桌子的任意数量的“实例”。

sql，带有内连接的sqlite SELECT

2 个答案: