add 597

fishercoder1534 · fishercoder1534 · commit 8adc6218aac9 · 2017-07-22T16:14:25.000-07:00
diff --git a/README.md b/README.md
@@ -569,6 +569,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |612|[Shortest Distance in a Plane](https://leetcode.com/problems/shortest-distance-in-a-plane/)|[Solution](../master/database/_612.sql) | || Medium|
 |610|[Triangle Judgement](https://leetcode.com/problems/triangle-judgement/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_610.java) | | | Easy | 
 |607|[Sales Person](https://leetcode.com/problems/sales-person/)|[Solution](../master/database/_607.sql) | | | Easy |
+|597|[Friend Requests I: Overall Acceptance Rate](https://leetcode.com/problems/friend-requests-i-overall-acceptance-rate/)|[Solution](../master/database/_597.sql) | | | Easy |
 |596|[Classes More Than 5 Students](https://leetcode.com/problems/classes-more-than-5-students/)|[Solution](../master/database/_596.sql) | || Easy |
 |595|[Big Countries](https://leetcode.com/problems/big-countries/)|[Solution](../master/database/_595.sql) | O(n) |O(1) | Easy |
 |586|[Customer Placing the Largest Number of Orders](https://leetcode.com/problems/customer-placing-the-largest-number-of-orders/)|[Solution](../master/database/_586.sql) | | | Easy|
diff --git a/database/_597.sql b/database/_597.sql
@@ -0,0 +1,15 @@
+--597. Friend Requests I: Overall Acceptance Rate
+
+select
+    round(
+        ifnull(
+        (select count(distinct requester_id,accepter_id) from request_accepted)
+        /
+        (select count(distinct sender_id, send_to_id) from friend_request)
+        ,0)
+    ,2)
+    as accept_rate;
+
+--The divisor (total number of requests) could be '0'
+--if the table friend_request is empty.
+--So, we have to utilize ifnull to deal with this special case.
