插入引用另一个表的值

Posted 2023-05-09

【中文标题】插入引用另一个表的值

【英文标题】：Insert values referring to another table

【发布时间】：2019-01-22 15:35:51

【问题描述】：

我创建了以下简单的datamodel：

我使用以下insert statements 插入值：

1) 表产品：

INSERT INTO test.products
(ProductName, Price)
VALUES 
("Product A","99,99"),
("Product B","49,95"), 
("Product C","5,95");

2) 表格订单：

INSERT INTO test.orders
(Customer)
VALUES 
("Customer A"),
("Customer B"), 
("Customer B");

到目前为止，这一切都很好。

---

但是，现在我还想将值插入到表 Products_per_Order 中。 正如您在datamodel 中看到的，Products_per_Order 表包含Price 列。在此列中，我想在Products_idProducts 列中插入引用ID 的价格。因此，我尝试使用以下insert statement，但到目前为止无法使其工作：

INSERT INTO test.products_per_order
(Orders_idOrders, Products_idProducts, Price, Quantity)
VALUES
("1","1",(Select Price from test.products),"5"),
("1","2",(Select Price from test.products),"4"),
("2","1",(Select Price from test.products),"10"),
("3","2",(Select Price from test.products),"3"),
("3","3",(Select Price from test.products),"9");

你知道如何解决这个问题吗？

【问题讨论】：

您的查询毫无意义。 应该为每一行插入哪个价格？

【参考方案1】：

您可以使用子查询从 Products 表中提取它。

("2","1","Select Price from test.products where test.products.idProducts = '1')","10");

【参考方案2】：

您很接近，但是当您拥有(Select Price from test.products) 时，您会从 test.products 表中选择所有价格。你需要让它返回一个值。

INSERT INTO test.products_per_order
(Orders_idOrders, Products_idProducts, Price, Quantity)
VALUES
("1","1",(Select Price from test.products WHERE test.products.idProducts = '1'),"5"),
("1","2",(Select Price from test.products WHERE test.products.idProducts = '2'),"4"),
("2","1",(Select Price from test.products WHERE test.products.idProducts = '1'),"10"),
("3","2",(Select Price from test.products WHERE test.products.idProducts = '2'),"3"),
("3","3",(Select Price from test.products WHERE test.products.idProducts = '3'),"9");

【参考方案3】：

我建议改用insert . . . select：

insert into test.products_per_order (Orders_idOrders, Products_idProducts, Price, Quantity)
    select x.idOrder, x.idProduct, p.price, x.qty
    from (select 1 as idOrder, 2 as idProduct, 5 as qty union all
          select 1 as idOrder, 2 as idProduct, 4 as qty union all
          . . .  -- I've left these out so you can see the structure of the query
          select 3 as idOrder, 3 as idProduct, 9 as qty
         ) x left join
         test.products p
         on p.idProducts = x.idProduct;

这大大降低了拼写错误导致错误价格的可能性。

【讨论】：

嗨，戈登，感谢您的回答。工作台在“）x左连接”行向我显示查询有问题（运行语句时我也收到错误代码：1064）。我试图放置，或；在选择语句之后但无法使其工作。

@Michi 。 . . mysql 绝对支持这种语法。也许您在最后一行留下了额外的union all。

非常感谢。现在它正在工作。我只需要更改“on p.idProduct = x.idProduct;”这一行因为缺少一个 s “on p.idProducts = x.idProduct;”。

嗨，戈登，您对此有什么想法吗：***.com/questions/54350789/…