Customers With Repeat Tickets

Return customers who raised more than one ticket, with the count.

Table schema

Tickets(id INT PRIMARY KEY, customer VARCHAR(10), agent VARCHAR(10), priority VARCHAR(6), opened_at DATETIME, closed_at DATETIME)

Sample data

id | customer | agent | priority | opened_at | closed_at
1 | Ann | Raj | high | 2026-08-01 09:00:00 | 2026-08-01 11:00:00
2 | Bob | Raj | low | 2026-08-01 10:00:00 | 2026-08-02 10:00:00
3 | Cy | Mia | high | 2026-08-02 08:00:00 | 2026-08-02 09:30:00
4 | Ann | Mia | low | 2026-08-03 12:00:00 | NULL
5 | Dee | Raj | high | 2026-08-03 13:00:00 | NULL