tcv-tclsbc
diff --git a/‎README.md
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+12-1Lines changed: 12 additions & 1 deletion
@@ -533,4 +533,15 @@ UNION
 SELECT 'High Salary' AS category, SUM(IF(income>50000,1,0)) AS accounts_count 
 FROM Accounts
 ```
-
+[626. Exchange Seats](https://leetcode.com/problems/exchange-seats/)
+```sql
+-- id, student
+-- swap every two consecutives
+-- num(students): odd? no swap for last one
+
+SELECT id, 
+CASE WHEN MOD(id,2)=0 THEN (LAG(student) OVER (ORDER BY id))
+ELSE (LEAD(student, 1, student) OVER (ORDER BY id))
+END AS 'Student'
+FROM Seat
+```