How to replace a UNION in a query for a view? - mysql

Question

I have created the following query to use in a view
SELECT
*
FROM
customers c
JOIN
customer_business cb
ON
c.customer_id = cb.customer_id
union
SELECT
*
FROM
customers c
LEFT JOIN
customer_business
ON
business_id=NULL;
It makes his work perfectly. It shows all customers with the business associated, and at the end, shows all customers with the info of the business in null.
customer_id | business_id
--------------------------------
1 | 1
2 | 1
2 | 2
1 | NULL
2 | NULL
3 | NULL
But the problem es that the UNION makes the view has very poor performace.
I tryed to do it with LEFT JOIN but doesnt shows al the customers with business in null, just the ones without any businesses associated
I know that the solution to speed up my view is to remove that UNION, but i cant figure out how.
Can anyone help me?
Thanks
EDIT
Here's an example
Customer Table
customer_id | name
--------------------------------
1 | test1
2 | test2
3 | test3
Customer_business Table
customer_business_id | customer_id | business_id
----------------------------------------------------------
1 | 1 | 1
2 | 1 | 2
3 | 1 | 3
4 | 2 | 1
5 | 2 | 2
Expected query result:
name | customer_id | business_id
----------------------------------------------------------
test1 | 1 | 1
test1 | 1 | 2
test1 | 1 | 3
test2 | 2 | 1
test2 | 2 | 2
test1 | 1 | NULL
test2 | 2 | NULL
test3 | 3 | NULL

Answer 1

Updating it based on the comments below and the output you want.
Note that I have used UNION ALL which is faster than UNION as UNION uses DISTINCT to get unique records which in your case doesn't apply. Also, make sure customer_id is PK in Customer table and try adding non-unique index on customer_id in Customer_Business table and it should help with performance.
SELECT name,
C.customer_id,
business_id
FROM Customer C
INNER JOIN Customer_Business CB
ON C.customer_id = CB.customer_id
UNION ALL
SELECT name,
C.customer_id,
NULL
FROM Customer C

Answer 2

Excluding the union which we know that is not performant the other thing that slows down you query is the statement in the second query ON idbusiness = NULL.
I propose to edit you query like this and see the performance as a view:
SELECT c.customer_id, idbusiness
FROM customers c
JOIN customer_business cb ON c.customer_id = cb.customer_id
UNION
SELECT customer_id, NULL
FROM customers c
EDIT:
Looking for an alternative you could try this, it should return the same output (i've changed null values with 0) but i don't think it's faster:
SELECT c.customer_id, idbusiness
FROM customers c
INNER JOIN (
SELECT customer_id, idbusiness
FROM customer_business
UNION
SELECT 0 , 0
)b ON ( c.customer_id = b.customer_id )
OR (
b.idbusiness =0
)
Eventually you could try to put into a view only the subquery b or delete the union by putting the values 0,0 as a record in table customer_business.