for the user

user@host ★ tmux new -s hello

user@tmux ★ tmux detach
[detached (from session hello)]

user@host ★ tmux ls
hello: 1 windows (created Mon Aug 12 12:32:46 2019)

user@host ★ tmux attach -t hello

user@host ★ mysql -u root -p mygroovydb < mygroovydb_backup.sql

user@tmux ★ tmux detach
[detached (from session hello)]

user@host★ tmux kill-session -t hello
user@host ★ tmux ls
no server running on /private/tmp/tmux-110522448/default

detach hotkeys for when a command is running:

ctrl+b

then:

d