SQL: Can't get unique names/users - mysql

Question

I have this query which works perfectly:
SELECT
u.id
, u.mobile
, u.name
, (NOW() - u.authenticationTime) AS authenticateTimeDifference
, u.IP
, c.providerid
, c.requestid
, c.status
, u.port
FROM contacts c
LEFT JOIN users u ON u.id =
IF (
c.providerid = 2
, c.requestid
, c.providerid
) WHERE (
c.providerid = 2
AND c.status = 1
)
OR c.requestid = 2
ORDER BY authenticateTimeDifference
Now I wanted to only select DISTINCT u.name fields (or unique users) so I changed u.name to DISTINCT(u.name) but I am getting error:
You have an error in your SQL syntax; check the manual that corresponds to your
MySQL server version for the right syntax to use near 'DISTINCT(u.name) ,
(NOW() - u.authenticationTime) AS au' at line 4
I also tried adding GROUP BY u.name but still no luck.
Can anybody tell how do I select unique names/users through above query ?
Thanks for the help

Answer 1

First, you need to use group by:
SELECT
u.id
, u.mobile
, u.name
, (NOW() - u.authenticationTime) AS authenticateTimeDifference
, u.IP
, c.providerid
, c.requestid
, c.status
, u.port
FROM contacts c
LEFT JOIN users u ON u.id =
IF (
c.providerid = 2
, c.requestid
, c.providerid
) WHERE (
c.providerid = 2
AND c.status = 1
)
OR c.requestid = 2
GROUP BY u.name
ORDER BY authenticateTimeDifference
Then you have to decide what to do with the other values. Should they show the lowest value, highest value, average, etc.? Since you want to group on the name only, you have to pick one for the fields not in the group by.

Answer 2

According to me Distinct must occur just after select. SO your query should be like this:-
SELECT DISTINCT u.id, u.mobile, u.name, (NOW() - u.authenticationTime) AS authenticateTimeDifference
, u.IP, c.providerid, c.requestid, c.status, u.port
FROM contacts c
LEFT JOIN users u ON u.id =
IF (c.providerid = 2, c.requestid, c.providerid)
WHERE (
c.providerid = 2
AND c.status = 1
)
OR c.requestid = 2
ORDER BY authenticateTimeDifference