MySQL select multiple id at the same time with php

Solution:

One simple approach uses aggregation:

SELECT idUser
FROM skills
WHERE idSkill IN (4, 9)
GROUP BY idUser
HAVING MIN(idSkill) <> MAX(idSkill);

The above query is sargable, meaning that an appropriate index can use the idSkill column. Consider adding this index for added performance:

CREATE INDEX idx ON skills (idUser, idSkill);

Edit:

Use this query for 3 items:

SELECT idUser
FROM skills
WHERE idSkill IN (2, 4, 9)
GROUP BY idUser
HAVING COUNT(DISTINCT idSkill) = 3;

Solution:

you can try this query. simply select userIds and add GROUP BY to avoid repeated userIds, and if you're using more skillIds like for example (4,9,2) then change the HAVING COUNT to 3 and so on.

SELECT idUser FROM your_table
WHERE idSkill IN (4, 9)
GROUP BY idUser
HAVING COUNT(DISTINCT idSkill) = 2

Solution:

One more solution:

SELECT DISTINCT idUser 
FROM tablename t0
WHERE EXISTS ( SELECT NULL
               FROM tablename t1
               WHERE t0.idUser = t1.idUser 
                 AND t1.idSkill = 4 )
  AND EXISTS ( SELECT NULL
               FROM tablename t2
               WHERE t0.idUser = t2.idUser 
                 AND t2.idSkill = 9 )

The solution can be expanded by adding more AND EXISTS () blocks if idSkill values list contains more than 2 values.

And this query is sargable. fiddle

Solution:

You can check with the below MYSQL Query :

SELECT DISTINCT(idUser) FROM skill WHERE idSkill IN(4,9)

Solution:

Try this:

SELECT DISTINCT(idUser) FROM skills
WHERE idSkill = 4 and idUser IN(select idUser from skills where idSkill = 9)