如何获取SQL中的行数

Question

I am a beginner regarding SQL queries so I hope that someone can help me with this.

I have a table that has 2 columns that are called MID and jachtID. What I need is the count of how many of the same jachtIDS there are with different MIDS attached to them like this:

MID   jachtID
89    10
95    10
83    11

The result should look something like this:

MID   jachtID  count
89    10       2
95    10       2
83    11       1

And I need this for all of the rows I have tried using

  SELECT count(DISTINCT jachtID) FROM table

But this just gives me 1 big number and not the result that I need.

Any help would be appreciated.

Answer 1

You can try the following query:

SELECT 
    T.MID,
    T.jachtID,
    jT.total
FROM table T INNER JOIN 
(
    SELECT 
    jachtID,
    COUNT(*) total
    FROM table 
    GROUP BY jachtID
)AS jT

ON T.jachtID = jT.jachtID 

---

First get count of each jachtID by the following query:

 SELECT 
   jachtID,
   COUNT(*) total
 FROM table 
 GROUP BY jachtID

Then make an INNER JOIN between the main table and the above query and get the corresponding jatchtID count thereby.

Answer 2

You might be able to do this with some GROUP BY magic, but I'm not sure, since you want all the rows. Using a sub query will work, though.

SELECT 
    a.MID, 
    a.jachtID,
    (SELECT count(b.jachtID) FROM table AS b WHERE b.jachtID= a.jachtID) AS `count` 
FROM table AS a