Retrieve data for multiple single or reference without like operator

Question

I have two tables, which looks like below. In the employee table instead mentioning the skills directly, I\'m using as reference from another table.

Question

Answer 1

Consider the following

mysql> select * from employee ;
+------+------+--------+
| id   | name | skills |
+------+------+--------+
|    1 | xyz  | 1,2,4  |
|    2 | abc  | 1,3    |
|    3 | lmn  | 1,2,3  |
+------+------+--------+
3 rows in set (0.00 sec)

mysql> select * from skillset ;
+------+----------+
| id   | skillset |
+------+----------+
|    1 | Python   |
|    2 | Java     |
|    3 | C        |
|    4 | PHP      |
+------+----------+
4 rows in set (0.00 sec)

This structure is similar to yours and to do query in these situation we can however use find_in_set but thats pretty inefficient , here are few examples

mysql> select e.id,
e.name, 
group_concat(s.skillset) as skillset 
from employee e join skillset s 
on find_in_set(s.id,e.skills) > 0 
where find_in_set(1,e.skills) > 0 
 group by e.id ;
+------+------+-----------------+
| id   | name | skillset        |
+------+------+-----------------+
|    1 | xyz  | Python,Java,PHP |
|    2 | abc  | C,Python        |
|    3 | lmn  | Java,Python,C   |
+------+------+-----------------+
3 rows in set (0.00 sec)

select e.id,
e.name, 
group_concat(s.skillset) as skillset 
from employee e 
join skillset s on find_in_set(s.id,e.skills) > 0 
where find_in_set(2,e.skills) > 0  group by e.id ;
+------+------+-----------------+
| id   | name | skillset        |
+------+------+-----------------+
|    1 | xyz  | Python,PHP,Java |
|    3 | lmn  | C,Java,Python   |
+------+------+-----------------+

Now a proper normalization would make life much simpler and will have the following association table

mysql> select * from employee_skills; 
+------------+----------+
| idemployee | idskills |
+------------+----------+
|          1 |        1 |
|          1 |        2 |
|          1 |        3 |
|          2 |        1 |
|          2 |        3 |
|          3 |        1 |
|          3 |        2 |
|          3 |        3 |
+------------+----------+

Now doing query will be much more efficient in this case

mysql> select e.id,
e.name,
s.skillset from employee e 
join employee_skills es on es.idemployee = e.id 
join skillset s on s.id = es.idskills where s.id = 1 ;
+------+------+----------+
| id   | name | skillset |
+------+------+----------+
|    1 | xyz  | Python   |
|    2 | abc  | Python   |
|    3 | lmn  | Python   |
+------+------+----------+

Using the last approach more complex calculations could be done pretty easily.

Answer 2

As mentioned by others in the comments, this is not the most useful design choice as it would make it long winded to create a simple CRUD interface to interact with these values.

You would have ideally:

employee table:

+-----+-------------+
| id  | name        |
+-----+-------------+
| 1   | Bob         |
| 2   | Mary        |
+-----+-------------++

skillset table:

+-----+-------------+
| id  | skillset    |
+-----+-------------+
| 1   | Python      |
| 2   | Java        |
| 3   | C           |
| 4   | PHP         |
+-----+-------------+

employee_skillset table:

+-----+---------------+---------------+
| id  | employee_id   | skillset_id   |
+-----+---------------+---------------+
| 1   | 1             | 1             |
| 2   | 1             | 2             |
| 3   | 1             | 4             |
| 4   | 2             | 1             |
| 5   | 2             | 3             |
+-----+---------------+---------------+

Then you could do:

SELECT *
FROM employee e
INNER JOIN employee_skillset es
ON e.id = es.employee_id    
WHERE es.skillset_id = "1";

You could use the skillset table in the CRUD interface as selectable / editable options.

EDIT:

It's easy enough to include a range of skills within this too using the IN clause:

WHERE es.skillset_id IN (1, 3, 4);