SQL子查询以从差异表获取信息

Question

So basically, im new to SQL doing practice tutorials to better expand my knowledge. But i im stuck on this few problems.

How would i write and SQL query to

Get the cities of agents booking an order for a customer whose cid is 'c006'.

&

Get the cids and names of customers who did not place an order through agent a03.

WITHOUT USING THE "JOIN" method.

Database snapshot: http://i.stack.imgur.com/XicJh.png

Answer 1

You can try this mate:

-- Q1
SELECT city FROM agents
WHERE aid IN (
    SELECT aid FROM orders
    WHERE cid = 'c006'
); 
-- Q2
SELECT cid, name FROM customers
WHERE cid NOT IN (
    SELECT cid FROM orders
    WHERE aid = 'a03'
);

Answer 2

Mainly you need to use join queries, your first query:

select a.city from Orders o 
inner join Agents a on a.aid = o.aid
where o.cid = 'c006'

The second one is similar, using the other tables and fields.