1select @@global.extra_port;
2@@global.extra_port
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4select @@session.extra_port;
5ERROR HY000: Variable 'extra_port' is a GLOBAL variable
6show global variables like 'extra_port';
7Variable_name	Value
8extra_port	0
9show session variables like 'extra_port';
10Variable_name	Value
11extra_port	0
12select * from information_schema.global_variables where variable_name='extra_port';
13VARIABLE_NAME	VARIABLE_VALUE
14EXTRA_PORT	0
15select * from information_schema.session_variables where variable_name='extra_port';
16VARIABLE_NAME	VARIABLE_VALUE
17EXTRA_PORT	0
18set global extra_port=1;
19ERROR HY000: Variable 'extra_port' is a read only variable
20set session extra_port=1;
21ERROR HY000: Variable 'extra_port' is a read only variable
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