How to Do a Max(Count(*)) in SQL

Can I do a max(count(*)) in SQL?

Use:

  SELECT m.yr, 
         COUNT(*) AS num_movies
    FROM MOVIE m
    JOIN CASTING c ON c.movieid = m.id
    JOIN ACTOR a ON a.id = c.actorid
                AND a.name = 'John Travolta'
GROUP BY m.yr
ORDER BY num_movies DESC, m.yr DESC

Ordering by num_movies DESC will put the highest values at the top of the resultset. If numerous years have the same count, the m.yr will place the most recent year at the top... until the next num_movies value changes.

Can I use a MAX(COUNT(*)) ?

No, you can not layer aggregate functions on top of one another in the same SELECT clause. The inner aggregate would have to be performed in a subquery. IE:

SELECT MAX(y.num)
  FROM (SELECT COUNT(*) AS num
          FROM TABLE x) y

SQL select MAX(COUNT)

I'd try with a ORDER BY max DESC LIMIT 1, where maximum is the count(*) field. Something like:

SELECT "name", count(*) maximum FROM "users" 
   INNER JOIN "microposts" ON "microposts"."user_id" = "users"."id" 
GROUP BY users.id 
ORDER BY maximum DESC 
LIMIT 1

I dont' have mysql available now, so I'm doing this on the paper (and it might not work), but it's just an orientation.

Using sub-queries in SQL to find max(count())

You don't need a correlated subquery for what you are doing. Here is one way based on your query:

select CustomerNum, count(CustomerNum)
from Rentals R
group by CustomerNum
having count(CustomerNum) = (select max(cnt)
                             from (select CustomerNum, count(CustomerNum) as cnt
                                   from Rentals
                                   group by CustomerNum
                                  ) rc
                            );

I would be inclined to move the subquery to the from clause and use subqueries:

select rc.*
from (select CustomerNum, count(CustomerNum) as cnt
      from Rentals R
      group by CustomerNum
     ) rc join
     (select max(cnt) as maxcnt
      from (select CustomerNum, count(CustomerNum) as cnt
            from Rentals
            group by CustomerNum
           ) rc
     ) m
     on rc.cnt = m.maxcnt;

These are standard SQL and should work in both systems. In practice, I'd probably find a way to use top or row_number() on SQL Server 2008.

Maximum Count of Distinct Values in SQL

You can do this with nested aggregation:

select max(cnt)
from (select person_id, count(*) as cnt
      from mytable
      group by person_id
     ) p;

If you actually want the person, you can also do:

select person_id, count(*) as cnt
from mytable
group by person_id
order by count(*) desc
limit 1;

SELECT id HAVING maximum count of id

SELECT color_id AS id, COUNT(color_id) AS count 
FROM products 
WHERE item_id = 1234 AND color_id IS NOT NULL 
GROUP BY color_id 
ORDER BY count DESC
LIMIT 1;

This will give you the color_id and the count on that color_id ordered by the count from greatest to least. I think this is what you want.

for your edit...

SELECT color_id, COUNT(*) FROM products WHERE color_id = 3;

how to multiply a numerical field in count in sql

Use sum() instead of count():

Select sum(node.weight) as count, ans.cn_gender, poll.pollname
From report.cm_marital_satisfaction ans Join
     poll_management.POLLES poll
     on ans.cn_pollId = poll.id Join
     poll_management.POSITIONS node
     on ans.cn_positionId = node.id
Where ans.cn_pollId in (113)
group by ans.cn_gender, poll.pollname

SUM of grouped COUNT in SQL Query

SELECT name, COUNT(name) AS count
FROM table
GROUP BY name

UNION ALL

SELECT 'SUM' name, COUNT(name)
FROM table

OUTPUT:

name                                               count
-------------------------------------------------- -----------
alpha                                              1
beta                                               3
Charlie                                            2
SUM                                                6

Fastest way to count exact number of rows in a very large table?

Simple answer:

Database vendor independent solution = use the standard = COUNT(*)
There are approximate SQL Server solutions but don't use COUNT(*) = out of scope

Notes:

COUNT(1) = COUNT(*) = COUNT(PrimaryKey) just in case

Edit:

SQL Server example (1.4 billion rows, 12 columns)

SELECT COUNT(*) FROM MyBigtable WITH (NOLOCK)
-- NOLOCK here is for me only to let me test for this answer: no more, no less

1 runs, 5:46 minutes, count = 1,401,659,700

--Note, sp_spaceused uses this DMV
SELECT
   Total_Rows= SUM(st.row_count)
FROM
   sys.dm_db_partition_stats st
WHERE
    object_name(object_id) = 'MyBigtable' AND (index_id < 2)

2 runs, both under 1 second, count = 1,401,659,670

The second one has less rows = wrong. Would be the same or more depending on writes (deletes are done out of hours here)

How to count number of records per day?

select DateAdded, count(CustID)
from Responses
WHERE DateAdded >=dateadd(day,datediff(day,0,GetDate())- 7,0)
GROUP BY DateAdded