SET @start_global_value = @@global.old_alter_table; SELECT @start_global_value; @start_global_value 0 select @@global.old_alter_table; @@global.old_alter_table 0 select @@session.old_alter_table; @@session.old_alter_table 0 show global variables like 'old_alter_table'; Variable_name Value old_alter_table OFF show session variables like 'old_alter_table'; Variable_name Value old_alter_table OFF select * from information_schema.global_variables where variable_name='old_alter_table'; VARIABLE_NAME VARIABLE_VALUE OLD_ALTER_TABLE OFF select * from information_schema.session_variables where variable_name='old_alter_table'; VARIABLE_NAME VARIABLE_VALUE OLD_ALTER_TABLE OFF set global old_alter_table=1; set session old_alter_table=ON; select @@global.old_alter_table; @@global.old_alter_table 1 select @@session.old_alter_table; @@session.old_alter_table 1 show global variables like 'old_alter_table'; Variable_name Value old_alter_table ON show session variables like 'old_alter_table'; Variable_name Value old_alter_table ON select * from information_schema.global_variables where variable_name='old_alter_table'; VARIABLE_NAME VARIABLE_VALUE OLD_ALTER_TABLE ON select * from information_schema.session_variables where variable_name='old_alter_table'; VARIABLE_NAME VARIABLE_VALUE OLD_ALTER_TABLE ON set global old_alter_table=1.1; ERROR 42000: Incorrect argument type to variable 'old_alter_table' set global old_alter_table=1e1; ERROR 42000: Incorrect argument type to variable 'old_alter_table' set global old_alter_table="foo"; ERROR 42000: Variable 'old_alter_table' can't be set to the value of 'foo' SET @@global.old_alter_table = @start_global_value; SELECT @@global.old_alter_table; @@global.old_alter_table 0