Find unmatched records with 2 foreign keys - mysql

Question

I have 2 tables:
table Companies
+----------+-------------+----+
| Id | MainId | Type | Name |
+----+--------+--------+------+
| 1 | | NO | |
| 2 | 1 | Filial | |
| 3 | | NO | |
| 4 | 3 | Filiar | |
+-------------+--------+------+
table Employees
+------------------+-------+-------+
| Id | Name | CompId| FilId |
+------------------+-------+-------+
| 333| Simon | 1 | |
| 444| John | 1 | 2 |
| 555| Andrew | | 4 |
| 777| Dennis | 11 | |
| 888| John | 3 | 10 |
+------------------+-------+-------+
How can I get all employees that work at companies listed in Companies table?
= At least one row (CompId or FilId) is linked to row in Companies table
How can I get all employees that DON'T work at companies listed in Companies table?
= BOTH CompId or FilId columns DON'T exist in Companies table
I have tried the solution but it doesn't perform well...
1st:
SELECT * FROM `Employees`
INNER JOIN `Companies` ON `Employees`.`FilId` = `Companies`.`Id`
OR `Employees`.`FilId` = `Companies`.`Id`
Added results for SHOW CREATE TABLE table_name
Removed unused columns
CREATE TABLE `Employees` (
`Id` varchar(10) NOT NULL,
`Name` varchar(255) NOT NULL
`CompId` varchar(10) NOT NULL,
`FilId` varchar(10) NOT NULL,
PRIMARY KEY (`Id`),
KEY `empl_to_comps` (`VuzId`),
KEY `empl_to_fils` (`FilId`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8
CREATE TABLE `Companies` (
`Id` varchar(10) NOT NULL DEFAULT '',
`MainId` varchar(10) DEFAULT '',
`Type` varchar(255) NOT NULL,
`Name` varchar(255) NOT NULL
PRIMARY KEY (`Id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8

Answer 1

SELECT DISTINCT e.*
FROM Employees e
JOIN Companies c ON c.Id IN (e.CompId, FilId);
SELECT e.*
FROM Employees e
LEFT JOIN Companies c ON c.Id IN (e.CompId, FilId)
WHERE c.Id IS NULL;
Update
Depending on data and indexes the following two queries might be faster. And though verbose, they are more expressive than the JOIN queries.
SELECT e.*
FROM Employees e
WHERE EXISTS (
SELECT *
FROM Companies c
WHERE c.Id = e.CompId
)
OR EXISTS (
SELECT *
FROM Companies c
WHERE c.Id = e.FilId
);
SELECT e.*
FROM Employees e
WHERE NOT EXISTS (
SELECT *
FROM Companies c
WHERE c.Id = e.CompId
)
AND NOT EXISTS (
SELECT *
FROM Companies c
WHERE c.Id = e.FilId
);