How to select MYSQL databases elements without an "array" match? - mysql

Question

I have 3 MYSQL tables, one with members information (with ids), one with subscription years (also with ids), and a join table to save every year each member have been subscribed (using years and members ids). I managed to get the list of all the members related to a specific year using the MYSQL code below, but I can't figure out how to get the list of members that are not related to the same years (the ones not included on the first list) using MYSQL code.
I already tried to search for the members without the specific year id, using the code below, but this will return a list with all the members except for the ones that were subscribed only on that year.
The code to extract all the member subscribed on a year knowing its year id (x):
SELECT DISTINCT m.id, first_name, last_name
FROM members_years sc
INNER JOIN members m ON m.id = sc.member_id
WHERE sc.year_id = x
While the nonworking code to extract the list of members not related with a subscription year knowing its year id (x):
SELECT DISTINCT m.id, first_name, last_name
FROM members_years sc
INNER JOIN members m ON m.id = sc.member_id
WHERE sc.year_id != x
To resume I need to extract using a single MYSQL code the list of all members that are not related with a specific subscription year.
Here an example of tables:
Members:
Id | First_name | Last_name
——————————————————
1 | John | Smith
——————————————————
2 | John | Doe
——————————————————
3 | Jane | Doe
Years:
Id | Year
——————
1 | 2013
——————
2 | 2014
——————
3 | 2015
Members_years:
Id | member_id | year_id
———————————————
1 | 1 | 1
———————————————
2 | 1 | 2
———————————————
3 | 2 | 3
———————————————
4 | 3 | 1
———————————————
5 | 3 | 2
———————————————
6 | 3 | 3
With the 3 previous tables, searching with x=3 (2015) with the first code we will get John Doe and Jane Doe, that is fine.
But with second code, using x=3, we get John Smith and Jane Doe instead of only Jonh Smith.

Answer 1

One way to do what you want is with a left join. You want to find all rows which don't have a particular relation for a year x
SELECT m.id, first_name, last_name
FROM members m
LEFT JOIN members_years sc ON (m.id = sc.member_id and sc.year_id = x)
WHERE sc.year_id IS NULL;
So, you LEFT JOIN members_years looking for rows with your target year for each member in the ON clause.
Any member which doesn't have that year would have NULL values from that join, so the WHERE clause looks for those and we end up with just the members you need.
If you're unfamiliar with LEFT JOIN, you might find it instructive to leave off the WHERE clause and include some columns from sc:
SELECT m.id, first_name, last_name, sc.year_id
FROM members m
LEFT JOIN members_years sc ON (m.id = sc.member_id and sc.year_id = x);
You'll get a row for every member - some with a value for year_id, some with NULL.

Answer 2

I think #IVO GELOV’s comment contains the code you are looking for. The reason you are seeing John Doe and Jane Doe pop up in the results of your second query is because both of those users have a record on members_years where year_id Is Not equal to 3. (Although John Doe doesn’t actually have a record where year_id Is Not equal to 3 in your example data, I am assuming that on the actual data you are querying against this is true). Your query needs to instead determine what users DO have a record where year_id Is Equal to 3, and then return every other user besides the users that meet this criteria in your search result.