Update ddl.sql

[hellower]

client_pid(worker_pid)

The server running pg_timetable may be different, but coincidentally the pid may be the same. At my docker enviroment, serveral same pid(differnt docker constainer) happended.

Duplicate execution can be prevented by adding the client_addr column as shown below.

SQL> select * from timetable.active_sessions client_id

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14 pg_timetable 28417 167.71.214.34 2022-08-07 14:12:24.333 +0900 14 pg_timetable 28418 167.71.214.34 2022-08-07 14:12:24.366 +0900 14 pg_timetable 28422 128.199.132.200 2022-08-07 14:12:29.563 +0900 14 pg_timetable 28423 128.199.132.200 2022-08-07 14:12:29.589 +0900