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Author: NamVr

1292-immediate-food-delivery-ii/README.md

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+<p>Table: <code>Delivery</code></p>
+
+<pre>
++-----------------------------+---------+
+| Column Name                 | Type    |
++-----------------------------+---------+
+| delivery_id                 | int     |
+| customer_id                 | int     |
+| order_date                  | date    |
+| customer_pref_delivery_date | date    |
++-----------------------------+---------+
+delivery_id is the column of unique values of this table.
+The table holds information about food delivery to customers that make orders at some date and specify a preferred delivery date (on the same order date or after it).
+</pre>
+
+<p>&nbsp;</p>
+
+<p>If the customer&#39;s preferred delivery date is the same as the order date, then the order is called <strong>immediate;</strong> otherwise, it is called <strong>scheduled</strong>.</p>
+
+<p>The <strong>first order</strong> of a customer is the order with the earliest order date that the customer made. It is guaranteed that a customer has precisely one first order.</p>
+
+<p>Write a solution to find the percentage of immediate orders in the first orders of all customers, <strong>rounded to 2 decimal places</strong>.</p>
+
+<p>The&nbsp;result format is in the following example.</p>
+
+<p>&nbsp;</p>
+<p><strong class="example">Example 1:</strong></p>
+
+<pre>
+<strong>Input:</strong> 
+Delivery table:
++-------------+-------------+------------+-----------------------------+
+| delivery_id | customer_id | order_date | customer_pref_delivery_date |
++-------------+-------------+------------+-----------------------------+
+| 1           | 1           | 2019-08-01 | 2019-08-02                  |
+| 2           | 2           | 2019-08-02 | 2019-08-02                  |
+| 3           | 1           | 2019-08-11 | 2019-08-12                  |
+| 4           | 3           | 2019-08-24 | 2019-08-24                  |
+| 5           | 3           | 2019-08-21 | 2019-08-22                  |
+| 6           | 2           | 2019-08-11 | 2019-08-13                  |
+| 7           | 4           | 2019-08-09 | 2019-08-09                  |
++-------------+-------------+------------+-----------------------------+
+<strong>Output:</strong> 
++----------------------+
+| immediate_percentage |
++----------------------+
+| 50.00                |
++----------------------+
+<strong>Explanation:</strong> 
+The customer id 1 has a first order with delivery id 1 and it is scheduled.
+The customer id 2 has a first order with delivery id 2 and it is immediate.
+The customer id 3 has a first order with delivery id 5 and it is scheduled.
+The customer id 4 has a first order with delivery id 7 and it is immediate.
+Hence, half the customers have immediate first orders.
+</pre>

1292-immediate-food-delivery-ii/solution.sql

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+# Write your MySQL query statement below
+
+# delivery_id is the primary key
+# first order = earliest order date.
+# immediate = same order and delivery date
+# scheduled = otherwise
+
+# return the percentage of immediate orders for first orders only , ROUND (2)
+# % means * 100. ROUND (VALUE * 100, 2)
+
+SELECT
+    ROUND(
+        SUM(
+            order_date = customer_pref_delivery_date -- This will evaluate to 0 or 1
+        ) / COUNT(
+            DISTINCT customer_id
+        ) * 100, 2
+    ) AS immediate_percentage
+FROM
+    Delivery
+WHERE (customer_id, order_date) IN (
+    SELECT customer_id, MIN(order_date)
+    FROM Delivery
+    GROUP BY customer_id
+);