Това може да работи
SELECT *
FROM users u
WHERE EXISTS (
SELECT *
FROM MainPage
WHERE CONCAT(',',doctors,',') LIKE CONCAT('%,',u.uid,',%')
AND Valid = 1
)
Това може да работи
SELECT *
FROM users u
WHERE EXISTS (
SELECT *
FROM MainPage
WHERE CONCAT(',',doctors,',') LIKE CONCAT('%,',u.uid,',%')
AND Valid = 1
)