MySQL-选择多个具有相同值的行，其中一个必须不同

Question

I have a table for IP addresses used and the associated userId. Now I know how I would select multiple entries of the same IP but how would I go about only selecting multiple entries WITH a different userId?

Answer 1

You can use conditional aggregation over each ip address and check to see if more than one user be associated with that ip address.

SELECT ip
FROM yourTable
GROUP BY ip
HAVING COUNT(DISTINCT userid) > 1    -- or a higher number if you want

Answer 2

you can use sql join do it for you INNER JOIN gets all records from one table that have some related entry in a second table

LEFT JOIN gets all records from the LEFT linked table but if you have selected some columns from the RIGHT table, if there is no related records, these columns will contain NULL

RIGHT JOIN is like the above but gets all records in the RIGHT table

FULL JOIN gets all records from both tables and puts NULL in the columns where related records do not exist in the opposite table

SQL joins