SQL - 根据另一个表中指定的条件限制一个表的结果

Question

This has been asked many times before, but I'm having trouble understanding previous solutions and implementing them into my own query. (I am very much still a SQL novice.)

I have the following query:

select *
from **Product** prod
inner JOIN
**account** acct on prod.product_id = acct.product_id
inner JOIN
**client_account_relationship** car on acct.account_id = car.ACCOUNT_ID
inner JOIN
**client** cl on car.client_id = cl.client_id
where prod.product_code != 'Producttype'

My table structure is as follows:

Product - This table contains what products a client account holds

Account - This table holds what accounts a client holds

Client Account Relationship - This table holds the link between clients and accounts

Client - This table holds clients

A Product will always have an Account, an Account will always have a Client/Account Relationship, and a Client/Account Relationship will always have a Client.

I want to show display all clients that do NOT hold a specific product type. Ie Show me all Clients that do not hold ProductType1. But because a Client can hold many different product types, my query will show me all the products except the one I'm excluding, but a client might still hold that excluded product.

How do I limit results from the Client Table based on criteria set in another table?

Answer 1

The nice thing about SQL being a descriptive language is that it translates from English quite nicely. You already described what you want to do - find all the clients that don't have a specific product. Translated to SQL, this would be the [not] exists operator:

SELECT *
FROM   client c
WHERE  NOT EXISTS (SELECT *
                   FROM   product p
                   JOIN   account a ON p.product_id = a.product_id
                   JOIN   client_account_relationship car ON 
                          a.account_id = car.ACCOUNT_ID
                   WHERE  car.client_id = c.client_id AND
                          p.product_code = 'Producttype')

Answer 2

Using NOT IN statement. Not in asks SQL to specifically exclude those product types which match the criteria in where condition in sub query

select distinct car.client_id
from **Product** prod
inner JOIN
**account** acct on prod.product_id = acct.product_id
inner JOIN
**client_account_relationship** car on acct.account_id = car.ACCOUNT_ID
inner JOIN
**client** cl on car.client_id = cl.client_id
where car.client_id not in 
(select car.client_id 
from **Product** prod
inner JOIN
**account** acct on prod.product_id = acct.product_id
inner JOIN
**client_account_relationship** car on acct.account_id = car.ACCOUNT_ID
inner JOIN
**client** cl on car.client_id = cl.client_id
where prod.product_code != 'ProductType1'
)