PHP MySQL How to get the count of rows where column is completely unique

Question

I have a table that looks like this

id          +        kID       
--------------------------
0           |         3
1           |         6
2           |         7
3           |         6
4           |         7
5           |         5

What I want to do is find the amount of rows where the kID occurs only once. So in this case the value of the variable should be 2 because kID: 3 and 5 occurs only once so i'm trying to count that while ignoring everything else. I am really stumped, thanks for any help.

Answer 1

This will show kID s that occur only once:

SELECT kID, COUNT(kID)
FROM table
GROUP BY kID
HAVING COUNT(kID) < 2

Result

| KID | COUNT(KID) |
--------------------
|   3 |          1 |
|   5 |          1 |

See the demo

Then to get the total count of those:

SELECT Count(*) AS count 
FROM   (SELECT kid, 
               Count(kid) 
        FROM   tbl 
        GROUP  BY kid 
        HAVING Count(kid) < 2) a

Result

| COUNT |
---------
|     2 |

See the demo

Answer 2

Try this

SELECT
  id,
  count(kID) as `Count`
FROM mytable as t
GROUP BY kID
HAVING Count = 1

Answer 3

How about

select count(*) from 
(select kid, count(*) from table group by kid having count(*) = 1)

Answer 4

You could do the following:

select count(*) from 
(
    select kID, COUNT(*) [c] from tableName
    group by kID
) t
where t.c = 1

Answer 5

SELECT kID, 
COUNT(kID) 
FROM tableName
GROUP BY kID
HAVING COUNT(kID) = 1

Answer 6

You could do it with a sub-select. This should work, though might not be extremely efficient:

SELECT id, kID, COUNT(1) FROM (SELECT COUNT(1),kID FROM TABLE
                               GROUP BY kID
                               HAVING COUNT = 1)

Answer 7

One more way to do it. It will work as long as the (id) is the primary key of the table or there is a unique constraint on (kid, id) :

SELECT COUNT(*) AS cnt
FROM
  ( SELECT NULL
    FROM tableX
    GROUP BY kid
    HAVING MIN(id) = MAX(id) 
  ) AS g ;

Tested at SQL-Fiddle

An index on (kid, id) will improve efficiency - and only one COUNT() will be done, not 2.