feat: add sql solution to lc problem: No.0584 (#762)

No.0584.Find Customer Referee

Author: Dhoni77

solution/0500-0599/0584.Find Customer Referee/README.md

@@ -45,7 +45,12 @@
 ### **SQL**
 
 ```sql
-
+SELECT 
+    name
+FROM
+    Customer
+WHERE
+    referee_id != 2 OR referee_id IS NULL;
 ```
 
 <!-- tabs:end -->

solution/0500-0599/0584.Find Customer Referee/README_EN.md

@@ -60,7 +60,12 @@ Customer table:
 ### **SQL**
 
 ```sql
-
+SELECT 
+    name
+FROM
+    Customer
+WHERE
+    referee_id != 2 OR referee_id IS NULL;
 ```
 
 <!-- tabs:end -->

solution/0500-0599/0584.Find Customer Referee/Solution.sql

@@ -0,0 +1,6 @@
+SELECT 
+    name
+FROM
+    Customer
+WHERE
+    referee_id != 2 OR referee_id IS NULL;