将列添加到一个表中另一个是COUNT个

Question

I have a list of subscribers in table Subscribers . Every time they receive a copy of their subscription, a new record is created in Subscriptions_Fulfilments for each Subscribers.ID .

I can create a table showing each Subscriber ID and the number of copies they received with the following query:

SELECT Sub_ID, COUNT(Sub_ID) fcount FROM `Subscriptions_Fulfilments` 
GROUP BY Sub_ID

But I need to create a compound query that returns Subscribers along with a column showing the COUNT(Sub_ID) of Subscriptions_Fulfilments .

So I have two questions:

A) How would you make a query to create a table that shows each Subscriber and the number of times they've received their subscription, based on the COUNT of that Subscriber's ID in Subscriptions_Fulfilments ?

B) I'm operating under the assumption that a single MySql query accomplishing this would be more efficient than, say, running two queries, the one above and a SELECT * FROM Subscriptions , and combining the resulting arrays in PHP. I have a feeling I know the answer but I'd like to positively learn something new today.

Unfortunately, after too many tries, I'm clearly not good enough at queries for this and I have very little past the above query to show for it. I apologize if this ends up being a dup, I searched long and hard before asking, but it's quite difficult to search precisely for Query help...

Answer 1

One of the big advantages of a relational database is the ability to do joins and combinations of the data in your tables in a way that allows for this functionality without having to actually store it in a separate table.

You can accomplish this with a subquery like this:

SELECT Subscribers.name, fulfilments.count FROM Subscribers
INNER JOIN (
     SELECT id, count(*) as count FROM Subscriptions_Fulfilments
     GROUP BY Sub_Id
 )fulfilments ON subscribers.id = fulfilments.id

This might not be 100% what you're looking for and I might have messed up your names, but hopefully this will start to get you in the neighborhood of being correct?

Answer 2

Here is a simple example showing the Subscribers ID and the no of subscription they have received. Hope it helps.

Step 1: select the ids from the Subscriber table
Step 2: select the no of counts of subscriptions received by each subscriber.
Step 3: Join both the table ON the basis of ID.

SELECT SubId, noSub FROM 
Subscribers sb JOIN (SELECT SubId AS sid, COUNT(*)AS noSub FROM Subscriptions_Fulfilments GROUP BY SubId)AS ss ON sb.SubId = ss.sid

Answer 3

Simply try execute this query:

Select distinct Sub_ID, count from (SELECT Sub_ID, COUNT(Sub_ID) fcount FROM Subscriptions_Fulfilments GROUP BY Sub_ID);