SQL ACCESS（有关查询的思想和帮助）

Question

I am new at access SQL and i need help with some query. What i want is to find those customers that prefer a car (manufacturer and model) from prefer_to_buy AND prefer_to_rent that no one else prefer.

For example if 2 customers prefer toyota aygo must not be in the result table.

customer(customer_id,name)

prefer_to_buy(customer_id,manufacturer,model)

prefer_to_rent(customer_id, manufacturer,model)

I have tried a lot of ways including exists and i know there must be about 2-3 subqueries but i cant get it to work, any ideas?

Answer 1

Your problem definition is very vague, so the answer is also sort of generic. You should try to create a Left Outer Join on customer table and, for example, a " prefer_to_buy " Table using customer_id as a join field, and include: customer_id,name from the left table and manufacturer,model from the right table. The same logic applies to prefer_to_rent Table: you can actually combine these 3 Tables in a single Access SQL query using the aforementioned Outer Joins.

Hope this may help. Best regards,enter code here

Answer 2

There are a couple of parts to cover here. First, you could use the union operator to treat prefer_to_buy and prefer_to_rent as a single table (possibly with an additional literal "column" to indicate preference type). Once you've done this, you could use the exists operator to make sure no other customers prefer this car:

SELECT c.name, p.manufacturer, p.model
FROM   customer c
JOIN   (SELECT customer_id, manufacturer, model
        FROM   prefer_to_buy
        UNION 
        SELECT customer_id, manufacturer, model
        FROM   prefer_to_buy) p ON c.customer_id = p.customer_id
WHERE  NOT EXISTS (SELECT *
                   FROM   prefer_to_buy pb
                   WHERE  c.customer_id != pb.customer_id AND
                          p.manufacturer = pb.manufacturer AND
                          p.model = pb.model) AND
        NOT EXISTS (SELECT *
                   FROM   prefer_to_rent pr
                   WHERE  c.customer_id != pr.customer_id AND
                          p.manufacturer = pr.manufacturer AND
                          p.model = pr.model)

Answer 3

First you need to do to two joins one on prefer_to_buy AND one on prefer_to_rent. Next, you need to check if any one else would like the same manufacturer and model. Do this with a exist

SELECT *
FROM customer AS c 
  JOIN prefer_to_buy AS pb ON c.customer_id = pb.customer_id 
  JOIN prefer_rent AS pr ON c.customer_id = pr.customer_id 
WHERE NOT EXISTS ( SELECT 'x' FROM prefer_to_buy AS pb1 WHERE pb.manufacturer = pb1.manufacturer AND pb.model = pb1.model AND pb.customer_id <> pb1.customer_id) 
 AND NOT EXISTS ( SELECT 'x' FROM prefer_to_rent AS pr1 WHERE pb.manufacturer = pr1.manufacturer AND pb.model = pr1.model AND pb.customer_id <> pr1.customer_id)