How to add a few restrictios to a query?

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我寻月下人不归
我寻月下人不归 2021-01-29 08:44

I have difficulty with syntax...

This is my query:

SELECT t.diapason,
       Count(*) AS \'number_of_users\'
FROM   (SELECT CASE
                 WHEN a         


        
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2条回答
  • 2021-01-29 09:09

    You add WHERE clause to filter.

    SELECT t.diapason,
           COUNT(*) AS 'number_of_users'
    FROM (
        SELECT 
            CASE
                WHEN amount < 200 THEN '0-200'
                WHEN amount >= 200 THEN '200 +'
            END AS diapason
        FROM   (
            SELECT payments.user_id, SUM(amount) AS amount
            FROM   payments
            INNER JOIN activity ON payments.user_id = activity.user_idAND activity.login_time = payments.payment_time
            WHERE activity.login_time BETWEEN '2018-01-10' AND '2018-01-12'
            GROUP  BY payments.user_id
        ) p
    ) t
    GROUP  BY t.diapason
    ORDER  BY number_of_users DESC;
    
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  • 2021-01-29 09:11

    I understand your question as this. You had 3 users (user_id=1,2,3) login in the period 01.01.2018-12.01.2018. Of those users, user_id 1 made 2 payments totalling 250, user_id 2 made 1 payment of 40, and user_id 3 made 0 payments so their total is 0. Hence there are 2 values in the range 0-200, and 1 in the range 200 +. If that is the correct understanding, this query will give you the desired results:

    SELECT CASE  
             WHEN amount < 200 THEN '0-200'
             WHEN amount >= 200 THEN '200 +'
           END AS diapason,
           COUNT(*) AS number_of_users
    FROM (SELECT a.user_id, COALESCE(SUM(p.amount), 0) AS amount
          FROM activity a
          LEFT JOIN payments p ON p.user_id = a.user_id
          WHERE a.login_time BETWEEN '01.01.2018' AND '12.01.2018'
          GROUP BY a.user_id) p
    GROUP BY diapason;
    

    Output:

    diapason    number_of_users
    0-200       2
    200 +       1
    

    SQLFiddle demo

    Update

    To add another row with the total number_of_users, just add WITH ROLLUP to the GROUP BY clause:

    SELECT CASE  
             WHEN amount < 200 THEN '0-200'
             WHEN amount >= 200 THEN '200 +'
           END AS diapason,
           COUNT(*) AS number_of_users
    FROM (SELECT a.user_id, COALESCE(SUM(p.amount), 0) AS amount
          FROM activity a
          LEFT JOIN payments p ON p.user_id = a.user_id
          WHERE a.login_time BETWEEN '01.01.2018' AND '12.01.2018'
          GROUP BY a.user_id) p
    GROUP BY diapason WITH ROLLUP
    

    Output:

    diapason    number_of_users
    0-200       2
    200 +       1
    (null)      3
    

    In your application framework you can use the fact that the diapason value is NULL to output something like Total instead.

    Updated SQLFiddle

    You can also do the same in MySQL (see this SQLFiddle) by wrapping this query up as a subquery and using a COALESCE on the diapason column. In that case the output would be:

    diapason    number_of_users
    0-200       2
    200 +       1
    Total       3
    
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