SET @save_key_buffer=@@key_buffer_size;
SELECT @@key_buffer_size, @@small.key_buffer_size;
@@key_buffer_size	@@small.key_buffer_size
2097152	131072
SET @@global.key_buffer_size=16*1024*1024;
SET @@global.default.key_buffer_size=16*1024*1024;
SET @@global.default.key_buffer_size=16*1024*1024;
SET @@global.small.key_buffer_size=1*1024*1024;
SET @@global.medium.key_buffer_size=4*1024*1024;
SET @@global.medium.key_buffer_size=0;
SET @@global.medium.key_buffer_size=0;
SHOW VARIABLES like "key_buffer_size";
Variable_name	Value
key_buffer_size	16777216
SELECT @@key_buffer_size;
@@key_buffer_size
16777216
SELECT @@global.key_buffer_size;
@@global.key_buffer_size
16777216
SELECT @@global.default.key_buffer_size;
@@global.default.key_buffer_size
16777216
SELECT @@global.default.`key_buffer_size`;
@@global.default.key_buffer_size
16777216
SELECT @@global.`default`.`key_buffer_size`;
@@global.default.key_buffer_size
16777216
SELECT @@`default`.key_buffer_size;
@@default.key_buffer_size
16777216
SELECT @@small.key_buffer_size;
@@small.key_buffer_size
1048576
SELECT @@medium.key_buffer_size;
@@medium.key_buffer_size
0
SET @@global.key_buffer_size=@save_key_buffer;
SELECT @@default.key_buffer_size;
ERROR 42000: You have an error in your SQL syntax.  Check the manual that corresponds to your MySQL server version for the right syntax to use near 'default.key_buffer_size' at line 1
SELECT @@skr.table_type="test";
ERROR HY000: Variable 'table_type' is not a variable component (Can't be used as XXXX.variable_name)