SET @start_global_value = @@global.join_buffer_space_limit;
select @@global.join_buffer_space_limit;
@@global.join_buffer_space_limit
2097152
select @@session.join_buffer_space_limit;
@@session.join_buffer_space_limit
2097152
show global variables like 'join_buffer_space_limit';
Variable_name	Value
join_buffer_space_limit	2097152
show session variables like 'join_buffer_space_limit';
Variable_name	Value
join_buffer_space_limit	2097152
select * from information_schema.global_variables where variable_name='join_buffer_space_limit';
VARIABLE_NAME	VARIABLE_VALUE
JOIN_BUFFER_SPACE_LIMIT	2097152
select * from information_schema.session_variables where variable_name='join_buffer_space_limit';
VARIABLE_NAME	VARIABLE_VALUE
JOIN_BUFFER_SPACE_LIMIT	2097152
set global join_buffer_space_limit=10;
Warnings:
Warning	1292	Truncated incorrect join_buffer_space_limit value: '10'
select @@global.join_buffer_space_limit;
@@global.join_buffer_space_limit
2048
set session join_buffer_space_limit=10;
Warnings:
Warning	1292	Truncated incorrect join_buffer_space_limit value: '10'
select @@session.join_buffer_space_limit;
@@session.join_buffer_space_limit
2048
set global join_buffer_space_limit=1.1;
ERROR 42000: Incorrect argument type to variable 'join_buffer_space_limit'
set session join_buffer_space_limit=1e1;
ERROR 42000: Incorrect argument type to variable 'join_buffer_space_limit'
set global join_buffer_space_limit="foo";
ERROR 42000: Incorrect argument type to variable 'join_buffer_space_limit'
set global join_buffer_space_limit=0;
Warnings:
Warning	1292	Truncated incorrect join_buffer_space_limit value: '0'
select @@global.join_buffer_space_limit;
@@global.join_buffer_space_limit
2048
set global join_buffer_space_limit=4095;
Warnings:
Warning	1292	Truncated incorrect join_buffer_space_limit value: '4095'
select @@global.join_buffer_space_limit;
@@global.join_buffer_space_limit
2048
set session join_buffer_space_limit=cast(-1 as unsigned int);
Warnings:
Note	1105	Cast to unsigned converted negative integer to it's positive complement
Warning	1292	Truncated incorrect join_buffer_space_limit value: '18446744073709551615'
select @@session.join_buffer_space_limit;
@@session.join_buffer_space_limit
18446744073709549568
SET @@global.join_buffer_space_limit = @start_global_value;