SET @start_global_value = @@global.join_cache_level;
select @@global.join_cache_level;
@@global.join_cache_level
2
select @@session.join_cache_level;
@@session.join_cache_level
2
show global variables like 'join_cache_level';
Variable_name	Value
join_cache_level	2
show session variables like 'join_cache_level';
Variable_name	Value
join_cache_level	2
select * from information_schema.global_variables where variable_name='join_cache_level';
VARIABLE_NAME	VARIABLE_VALUE
JOIN_CACHE_LEVEL	2
select * from information_schema.session_variables where variable_name='join_cache_level';
VARIABLE_NAME	VARIABLE_VALUE
JOIN_CACHE_LEVEL	2
set global join_cache_level=4;
select @@global.join_cache_level;
@@global.join_cache_level
4
set session join_cache_level=4;
select @@session.join_cache_level;
@@session.join_cache_level
4
set global join_cache_level=1.1;
ERROR 42000: Incorrect argument type to variable 'join_cache_level'
set session join_cache_level=1e1;
ERROR 42000: Incorrect argument type to variable 'join_cache_level'
set global join_cache_level="foo";
ERROR 42000: Incorrect argument type to variable 'join_cache_level'
set global join_cache_level=0;
select @@global.join_cache_level;
@@global.join_cache_level
0
set session join_cache_level=cast(-1 as unsigned int);
Warnings:
Note	1105	Cast to unsigned converted negative integer to it's positive complement
Warning	1292	Truncated incorrect join_cache_level value: '18446744073709551615'
select @@session.join_cache_level;
@@session.join_cache_level
8
SET @@global.join_cache_level = @start_global_value;