MYSQL selecting users with specific skills
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20-09-2019 - |
Question
I'm muddling my way through by far the most complex SQL query i've ever done, which is probably extremely simple for most of you (:
I have three tables, User, Skills and User_Skills. The fields of which should be fairly self explanatory.
I want to choose people who have one or more skills that meet my criteria.
I can select a user with the skill i'm after, but i'm not sure about the syntax for querying multiple skills.
I'd like to just use one query, so I'm trying to use GROUP_CONCAT
Here's my SQL:
SELECT User_id, first_name, last_name, county, GROUP_CONCAT(CAST(Skill_id AS CHAR))
FROM User LEFT JOIN User_Skills ON User.id = User_Skills.User_id
LEFT JOIN Skills ON User_Skills.Skill_id = Skills.id GROUP BY User_id
User_id first_name last_name county GROUP_CONCAT(CAST(Skill_id AS CHAR))
1000 Joe Blow West Yorkshire 8,6,1,9,7,3,5,10
1001 Fred Bloggs COUNTY1 5,8,2,7,9
1003 asdf asdf1 Some County 10,8,2
How do I limit the search to only people who have skill 5 AND 9 ?
Solution
SELECT *
FROM users u
WHERE EXISTS
(
SELECT NULL
FROM user_skills us
WHERE us.skill_id IN (5, 9)
AND us.user_id = u.id
LIMIT 1, 1
)
This relies on the fact that (user_id, skill_id)
is a PRIMARY KEY
or a UNIQUE
key (that is you cannot assign a skill to a user more than once).
Update:
To return all skills (comma separated):
SELECT u.*,
(
SELECT GROUP_CONCAT(skill_id)
FROM user_skills uso
WHERE uso.user_ud = u.user_id
) AS all_skills
FROM users u
WHERE EXISTS
(
SELECT NULL
FROM user_skills us
WHERE us.skill_id IN (5, 9)
AND us.user_id = u.id
LIMIT 1, 1
)
OTHER TIPS
SELECT User_id, first_name, last_name, county, GROUP_CONCAT(CAST(Skill_id AS CHAR))
FROM User JOIN User_Skills ON User.id = User_Skills.User_id
JOIN Skills ON User_Skills.Skill_id IN (5,9)
GROUP BY User_id
If you want to prevent multiple skill records, then you may need a subquery
SELECT User_id, first_name, last_name, county,
(
SELECT (GROUP_CONCAT(CAST(subSkill.Skill_id AS CHAR))
FROM Skills as subSkill WHERE subSkill.skill_id = User_Skills.skill_id
GROUP BY subSkill.skill_id
)
FROM User JOIN User_Skills ON User.id = User_Skills.User_id
JOIN Skills ON User_Skills.Skill_id IN (5,9)
GROUP BY User_id
Why can't you just use an INNER JOIN inplace of the LEFT join, and issue a WHERE clause for the required skills?
SELECT User_id, first_name, last_name, county, GROUP_CONCAT(CAST(Skill_id AS CHAR))
FROM User
INNER JOIN User_Skills ON User.id = User_Skills.User_id
INNER JOIN Skills ON User_Skills.Skill_id = Skills.id GROUP BY User_id
WHERE skill_id = 5 OR skill_id=9
Here's how (will give you users with skills 5 AND 9):
SELECT User_id, first_name, last_name, county FROM User INNER JOIN User_Skills ON User.id = User_Skills.User_id INNER JOIN Skills ON User_Skills.Skill_id = Skills.id WHERE Skills.Skill_id = 5 AND Skills.Skill_id = 9 GROUP BY User_id
You just need a
HAVING FIND_IN_SET('5', skills) AND FIND_IN_SET('9', skills)
after the group by (where "skills" is the name of the grouped column). So your query should now look like
SELECT User_id, first_name, last_name, county, GROUP_CONCAT(CAST(Skill_id AS CHAR)) as skills
FROM User LEFT JOIN User_Skills ON User.id = User_Skills.User_id
LEFT JOIN Skills ON User_Skills.Skill_id = Skills.id GROUP BY User_id
HAVING FIND_IN_SET('5', skills) AND FIND_IN_SET('9', skills)