如何比较同一表中的列值/行

Question

It should pull the count of users_id where for the firstname/lastname of users is different for each of the user id.

here it should result 2 records( 1 & 7).

Answer 1

I believe you want:

select user_id
from t
group by user_id
having count(*) = count(distinct firstname) and
       count(*) = count(distinct lastname);

I'm not sure if you want the names as pair. If so:

having count(*) = count(distinct firstname, lastname)

Not all databases support multiple arguments to count(distinct) . If this is what you really intend, it is easy enough to phrase without using this.

Answer 2

 select user_id,count(*)
 from table 
 group by user_id having 
 count(distinct firstname) =count(firstname) and count(distinct 
 lastname)=count(lastname) ;

This gives those userids where on grouping userids if distinct fname and lname are greater than 1 for each userid group that means that group contains no duplicates.

Answer 3

Following SQL will work - it will also work if you would add lets say this row to your sample data (8,7, 'will', 'Rj') making User_id 7 having 4 rows but two of them with identical names.

with temp as (
SELECT user_id, firstname, lastname 
     , count(*) over (partition by user_id, firstname, lastname) as counter
 FROM t2
) 
SELECT * --distinct user_id
FROM temp t
WHERE not exists (SELECT 1 FROM temp WHEE counter = 2 and user_id = t.user_id)

The statements returns all rows with names unless you change the * to the commented distinct user_id then it will only return the user_id having ONLY unique names.