Supply user host pairs to be excluded from mysql results - mysql

Question

Data to work with:
+-------------+-------------+
| user | host |
+-------------+-------------+
| user1 | host1 | -
| user1 | ip1 | -
| user1 | host2 | *
| user2 | host2 | -
| user2 | ip2 | -
| unknown | unknown | +
| user1 | unknown | +
| unknown | host | +
+-------------+-------------+
The symbol to the right of the table are:
- do not show | + show as they are unknown | * because a user can only connect to one host, unless I had authorised it in which case I would supply the user host pair to the call also and it would not show.
Thats how I want things to work anyway.
This is where I am at with help from my question and as there is now a further condition a new question needs asking.
Current procedure
USE mysql;
DROP PROCEDURE IF EXISTS ShowUsers;
DELIMITER $
CREATE PROCEDURE `ShowUsers`(
IN KnownUsers varchar(500),
IN KnownHosts varchar(500)
)
BEGIN
SELECT
user,host
FROM
user
WHERE
NOT FIND_IN_SET(host, KnownHosts)
AND
NOT FIND_IN_SET(user, KnownUsers)
ORDER BY user, host ASC;
END $
DELIMITER ;
Calling the procedure like this
# known users and known hostnames or ips to match and exclude from results.
SET #Usernames = 'user1,user2';
SET #Hostnames = 'host1,host2,ip1,ip2'
CALL ShowUsers(#Usernames, #Hostnames);
Intended Result:
+-------------+-------------+
| user | host |
+-------------+-------------+
| user1 | host2 | *
| unknown | unknown | +
| user1 | unknown | +
| unknown | host | +
+-------------+-------------+
I want to be able to supply multiple user:host pairs of (known legitimate credentials) and return results that do not match, so return only suspect/illegitimate credentials in the query results.
I have created a fiddle https://www.db-fiddle.com/f/xb7dWXbkokHGbcPdzR7BUa/4 Hopefully you can see where I am going with this.

Answer 1

Based on whatever I could understand from your problem statement, you will need to use multiple string operations to satisfy your conditions (explanation in inline comments below):
Query
SELECT
`user`,`host`
FROM
tbl
WHERE
-- NOT condition to avoid returning one-to-one mapping between `user` and `host`
-- If `user` exist in the #Usernames, and the position of the
-- `user` matches with the position of the `host` in the #Hostnames
NOT (
FIND_IN_SET(`user`, #Usernames) > 0
-- Host and User are at same position in the lists
AND FIND_IN_SET(`user`, #Usernames) = FIND_IN_SET(`host`, #Hostnames)
)
AND
-- NOT condition to handle `host` at the end of #Hostnames list, where
-- there is no corresponding `user` mapped
NOT (
FIND_IN_SET(`host`, #Hostnames) > CHAR_LENGTH(#Usernames)
- CHAR_LENGTH(REPLACE(#Usernames, ',', ''))
+ 1
);
Result
| user | host |
| ------- | ------- |
| user1 | host2 |
| unknown | unknown |
| user1 | unknown |
| unknown | host |
View on DB Fiddle
Caveat: Above query will not work when there is no user in the #Usernames list. For brevity purpose, I avoided making the conditions more complex to handle that. Moreover, I doubt that in your practical use-case, you would have a situation where there are no user in the list.

Answer 2

This construct works (but not efficiently for huge tables):
WHERE (user, host) NOT IN ( ('u1', 'h1'), ('u2', 'h2), ... )
For further discussion, see "row constructor".