Multiple where clauses in select and insert - mysql

Question

So I have a 2 tables inside of the database. The first is just a unique ID to name mapping
Customers
UID | CustomerName
In a second table I have something like the following
Orders
OrderNum | CustomerID | CustomerID2
Now I would like to insert into orders, but I only have the name of the 2 customer names, so I'm imagining something like the following (which doesnt work)
insert into Orders select null, UID as id1, UID as id2 from Customers where CustomerName=="sven";
How can I go about getting the two UID's from the first table?
Also I need to be able to do the reverse and select from the table
SELECT * FROM Orders a JOIN (Customers b) ON a.UID=b.UID WHERE b.CustomerName='sven'
Neither of these work, and I can't seem to find something similar online strangely.

Answer 1

UPDATE: Based on your comments if you're trying to insert two different customers' ids to one order you can do
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
To select an order where one of the customers exists
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')
Here is SQLFiddle demo
Original answer: Are you looking for this?
To insert
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
To select
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'
Here is SQLFiddle demo

Answer 2

To insert into one table from another table use this syntax:
INSERT [LOW_PRIORITY | HIGH_PRIORITY] [IGNORE]
[INTO] tbl_name [(col_name,...)]
SELECT ...
[ ON DUPLICATE KEY UPDATE col_name=expr, ... ]
So in your case your query should be:
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT UID, UID
FROM Customers WHERE CustomerName = 'sven';
If you want to insert multiple record from a single query you can use IN operator instead of = like this:
INSERT INTO Orders (CustomerID, CustomerID2)
SELECT UID, UID
FROM Customers WHERE CustomerName IN ('sven', 'smith');
There is a mistake in your join in the SELECT query:
You joined both tables with UID while there is no UID in Orders table. May be you mean CustomerID. Try this one:
SELECT * FROM Orders a
JOIN Customers b
ON a.CustomerID = b.UID
WHERE b.CustomerName='sven'
See this SQLFiddle