所以我在数据库中有 2 个表。第一个只是一个唯一的 ID 到名称的映射
Customers
UID | CustomerName
在第二张表中，我有以下内容
Orders
OrderNum | CustomerID | CustomerID2
现在我想插入订单，但我只有 2 个客户名称的名称，所以我想像下面这样（这不起作用）
insert into Orders select null, UID as id1, UID as id2 from Customers where CustomerName=="sven";
我怎样才能从第一个表中获取两个 UID？
我还需要能够做相反的事情并从表中选择
SELECT * FROM Orders a JOIN (Customers b) ON a.UID=b.UID WHERE b.CustomerName='sven'
这些都不起作用，我似乎无法在网上找到类似的东西。
更新：根据您的评论，如果您尝试将两个不同客户的 ID 插入到一个订单中，您可以这样做
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT c1.uid uid1, c2.uid uid2
FROM
(
SELECT uid
FROM customers
WHERE customername = 'sven'
LIMIT 1
) c1 CROSS JOIN
(
SELECT uid
FROM customers
WHERE customername = 'jhon'
LIMIT 1
) c2
选择其中一个客户存在的订单
SELECT o.*
FROM orders o LEFT JOIN customers c1
ON o.customerid = c1.uid LEFT JOIN customers c2
ON o.customerid2 = c2.uid
WHERE c1.customername IN('sven', 'jhon')
OR c2.customername IN('sven', 'jhon')
这是SQLFiddle演示
原始答案：你在找这个吗？
插入
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT c1.uid uid1, c2.uid uid2
FROM customers c1 LEFT JOIN customers c2
ON c1.customername = c2.customername
AND c1.uid < c2.uid
WHERE c1.customername = 'sven'
LIMIT 1
选择
SELECT o.*
FROM orders o LEFT JOIN customers c1
ON o.customerid = c1.uid LEFT JOIN customers c2
ON o.customerid2 = c2.uid
WHERE c1.customername = 'sven'
OR c2.customername = 'sven'
这是SQLFiddle演示
要从另一个表插入一个表，请使用以下语法：
INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name [(col_name,...)]
SELECT ...
[ ON DUPLICATE KEY UPDATE col_name=expr, ... ]
因此，在您的情况下，您的查询应该是：
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT UID, UID
FROM Customers WHERE CustomerName = 'sven';
如果要从单个查询中插入多条记录，可以使用IN运算符而不是=这样：
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT UID, UID
FROM Customers WHERE CustomerName IN ('sven', 'smith');
您在SELECT查询中加入错误：
您加入了两个表，而表中UID没有。可能是你的意思。试试这个：UIDOrdersCustomerID
SELECT * FROM Orders a
JOIN Customers b
ON a.CustomerID = b.UID
WHERE b.CustomerName='sven'