callmebob :
I have Client and Invoice tables. They have one-to-many relationship, where Client.id = Invoice.client_id.
Client columns:
- id
Invoice columns:
- id,
- client_id,
- invoice_date
Of course the example is simplified to relevant data.
I am trying to select customers who did NOT have invoices after '2010-01-01'.
I can't figure out any working way to do this. Some routes I took look like this (there many other variations, but no point displaying the here):
SELECT c.id, COUNT(i.invoice_date > "2010-01-01") AS cnt
FROM Client AS c LEFT JOIN Invoice i ON i.client_id = c.id
GROUP BY c.id HAVING cnt = 0
and
SELECT client_id, COUNT(invoice_date > '2010-01-01') as cnt
FROM Invoice
GROUP BY client_id HAVING cnt = 0
Sebastian Brosch :
You can use a sub-query with NOT EXISTS like this:
SELECT *
FROM Client
WHERE NOT EXISTS (
SELECT 1
FROM Invoice
WHERE Invoice.invoice_date > '2010-01-01' AND Invoice.client_id = Client.id
)
You can also use SUM with CASE or IF:
-- CASE
SELECT c.id, SUM(CASE WHEN i.invoice_date > '2010-01-01' THEN 1 ELSE 0 END) AS cnt
FROM Client AS c LEFT JOIN Invoice i ON i.client_id = c.id
GROUP BY c.id
HAVING cnt = 0
-- IF
SELECT c.id, SUM(IF(i.invoice_date > '2010-01-01', 1, 0)) AS cnt
FROM Client AS c LEFT JOIN Invoice i ON i.client_id = c.id
GROUP BY c.id
HAVING cnt = 0
You can also use COUNT, but with CASE or IF:
-- CASE
SELECT client_id, COUNT(CASE WHEN invoice_date > '2010-01-01' THEN 1 ELSE NULL END) as cnt
FROM Invoice
GROUP BY client_id HAVING cnt = 0
-- IF
SELECT client_id, COUNT(IF(invoice_date > '2010-01-01', 1, NULL)) as cnt
FROM Invoice
GROUP BY client_id HAVING cnt = 0