drop table if exists t1,t2; set @`test`=1,@TEST=3,@select=2,@t5=1.23456; select @test,@`select`,@TEST,@not_used; @test @`select` @TEST @not_used 1 2 3 NULL set @test_int=10,@test_double=1e-10,@test_string="abcdeghi",@test_string2="abcdefghij",@select=NULL; select @test_int,@test_double,@test_string,@test_string2,@select; @test_int @test_double @test_string @test_string2 @select 10 1e-10 abcdeghi abcdefghij NULL set @test_int="hello",@test_double="hello",@test_string="hello",@test_string2="hello"; select @test_int,@test_double,@test_string,@test_string2; @test_int @test_double @test_string @test_string2 hello hello hello hello set @test_int="hellohello",@test_double="hellohello",@test_string="hellohello",@test_string2="hellohello"; select @test_int,@test_double,@test_string,@test_string2; @test_int @test_double @test_string @test_string2 hellohello hellohello hellohello hellohello set @test_int=null,@test_double=null,@test_string=null,@test_string2=null; select @test_int,@test_double,@test_string,@test_string2; @test_int @test_double @test_string @test_string2 NULL NULL NULL NULL select @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3; @t1:=(@t2:=1)+@t3:=4 @t1 @t2 @t3 5 5 1 4 select @t5; @t5 1.23456 CREATE TABLE t1 (c_id INT(4) NOT NULL, c_name CHAR(20), c_country CHAR(3), PRIMARY KEY(c_id)); INSERT INTO t1 VALUES (1,'Bozo','USA'),(2,'Ronald','USA'),(3,'Kinko','IRE'),(4,'Mr. Floppy','GB'); SELECT @min_cid:=min(c_id), @max_cid:=max(c_id) from t1; @min_cid:=min(c_id) @max_cid:=max(c_id) 1 4 SELECT * FROM t1 WHERE c_id=@min_cid OR c_id=@max_cid; c_id c_name c_country 1 Bozo USA 4 Mr. Floppy GB SELECT * FROM t1 WHERE c_id=@min_cid OR c_id=@max_cid OR c_id=666; c_id c_name c_country 1 Bozo USA 4 Mr. Floppy GB ALTER TABLE t1 DROP PRIMARY KEY; select * from t1 where c_id=@min_cid OR c_id=@max_cid; c_id c_name c_country 1 Bozo USA 4 Mr. Floppy GB drop table t1; set max_join_size=100; show variables like 'max_join_size'; Variable_name Value max_join_size 100 show global variables like 'max_join_size'; Variable_name Value max_join_size HA_POS_ERROR set GLOBAL max_join_size=2000; show global variables like 'max_join_size'; Variable_name Value max_join_size 2000 set max_join_size=DEFAULT; show variables like 'max_join_size'; Variable_name Value max_join_size 2000 set GLOBAL max_join_size=DEFAULT; show global variables like 'max_join_size'; Variable_name Value max_join_size HA_POS_ERROR set @@max_join_size=1000, @@global.max_join_size=2000; select @@local.max_join_size, @@global.max_join_size; @@session.max_join_size @@global.max_join_size 1000 2000 select @@identity, length(@@version)>0; @@identity length(@@version)>0 0 1 select @@VERSION=version(); @@VERSION=version() 1 select last_insert_id(345); last_insert_id(345) 345 select @@IDENTITY,last_insert_id(), @@identity; @@identity last_insert_id() @@identity 345 345 345 set big_tables=OFF, big_tables=ON, big_tables=0, big_tables=1, big_tables="OFF", big_tables="ON"; set global concurrent_insert=ON; show variables like 'concurrent_insert'; Variable_name Value concurrent_insert ON set global concurrent_insert=1; show variables like 'concurrent_insert'; Variable_name Value concurrent_insert ON set global concurrent_insert=0; show variables like 'concurrent_insert'; Variable_name Value concurrent_insert OFF set global concurrent_insert=OFF; show variables like 'concurrent_insert'; Variable_name Value concurrent_insert OFF set global concurrent_insert=DEFAULT; show variables like 'concurrent_insert'; Variable_name Value concurrent_insert ON set table_type=MYISAM, table_type="HEAP", global table_type="INNODB"; show local variables like 'table_type'; Variable_name Value table_type HEAP show global variables like 'table_type'; Variable_name Value table_type INNODB set GLOBAL query_cache_size=100000; set myisam_max_sort_file_size=10000, GLOBAL myisam_max_sort_file_size=20000; show variables like 'myisam_max_sort_file_size'; Variable_name Value myisam_max_sort_file_size 10000 show global variables like 'myisam_max_sort_file_size'; Variable_name Value myisam_max_sort_file_size 20000 set myisam_max_sort_file_size=default; show variables like 'myisam_max_sort_file_size'; Variable_name Value myisam_max_sort_file_size 20000 set global net_retry_count=10, session net_retry_count=10; set global net_buffer_length=1024, net_write_timeout=200, net_read_timeout=300; set session net_buffer_length=2048, net_write_timeout=500, net_read_timeout=600; show global variables like 'net_%'; Variable_name Value net_buffer_length 1024 net_read_timeout 300 net_retry_count 10 net_write_timeout 200 show session variables like 'net_%'; Variable_name Value net_buffer_length 2048 net_read_timeout 600 net_retry_count 10 net_write_timeout 500 set session net_buffer_length=8000, global net_read_timeout=900, net_write_timeout=1000; show global variables like 'net_%'; Variable_name Value net_buffer_length 1024 net_read_timeout 900 net_retry_count 10 net_write_timeout 1000 show session variables like 'net_%'; Variable_name Value net_buffer_length 7168 net_read_timeout 600 net_retry_count 10 net_write_timeout 500 set net_buffer_length=1; show variables like 'net_buffer_length'; Variable_name Value net_buffer_length 1024 set net_buffer_length=2000000000; show variables like 'net_buffer_length'; Variable_name Value net_buffer_length 1048576 set GLOBAL character set cp1251_koi8; show global variables like "client_collation"; Variable_name Value client_collation cp1251 set character set cp1251_koi8; show variables like "client_collation"; Variable_name Value client_collation cp1251 set global character set default, session character set default; show variables like "client_collation"; Variable_name Value client_collation latin1 select @@timestamp>0; @@timestamp>0 1 set @@rand_seed1=10000000,@@rand_seed2=1000000; select ROUND(RAND(),5); ROUND(RAND(),5) 0.02887 set big_tables=OFFF; Variable 'big_tables' can't be set to the value of 'OFFF' set big_tables="OFFF"; Variable 'big_tables' can't be set to the value of 'OFFF' set unknown_variable=1; Unknown system variable 'unknown_variable' set max_join_size="hello"; Wrong argument type to variable 'max_join_size' set table_type=UNKNOWN_TABLE_TYPE; Variable 'table_type' can't be set to the value of 'UNKNOWN_TABLE_TYPE' set table_type=INNODB, big_tables=2; Variable 'big_tables' can't be set to the value of '2' show local variables like 'table_type'; Variable_name Value table_type HEAP set SESSION query_cache_size=10000; Variable 'query_cache_size' is a GLOBAL variable and should be set with SET GLOBAL set GLOBAL table_type=DEFAULT; Variable 'table_type' doesn't have a default value set client_collation=UNKNOWN_CHARACTER_SET; Unknown character set: 'UNKNOWN_CHARACTER_SET' set character set unknown; Unknown character set: 'unknown' set character set 0; Wrong argument type to variable 'client_collation' set global autocommit=1; Variable 'autocommit' is a LOCAL variable and can't be used with SET GLOBAL select @@global.timestamp; Variable 'timestamp' is a LOCAL variable and can't be used with SET GLOBAL set @@version=''; Unknown system variable 'version' set @@concurrent_insert=1; Variable 'concurrent_insert' is a GLOBAL variable and should be set with SET GLOBAL set @@global.sql_auto_is_null=1; Variable 'sql_auto_is_null' is a LOCAL variable and can't be used with SET GLOBAL select @@global.sql_auto_is_null; Variable 'sql_auto_is_null' is a LOCAL variable and can't be used with SET GLOBAL set autocommit=1; set big_tables=1; select @@autocommit, @@big_tables; @@autocommit @@big_tables 1 1 set global binlog_cache_size=100; set bulk_insert_buffer_size=100; set character set cp1251_koi8; set character set default; set @@global.concurrent_insert=1; set global connect_timeout=100; select @@delay_key_write; @@delay_key_write ON set global delay_key_write="OFF"; select @@delay_key_write; @@delay_key_write OFF set global delay_key_write=ALL; select @@delay_key_write; @@delay_key_write ALL set global delay_key_write=1; select @@delay_key_write; @@delay_key_write ON set global delayed_insert_limit=100; set global delayed_insert_timeout=100; set global delayed_queue_size=100; set global flush=1; set global flush_time=100; set insert_id=1; set interactive_timeout=100; set join_buffer_size=100; set last_insert_id=1; set global local_infile=1; set long_query_time=100; set low_priority_updates=1; set max_allowed_packet=100; set global max_binlog_cache_size=100; set global max_binlog_size=100; set global max_connect_errors=100; set global max_connections=100; set global max_delayed_threads=100; set max_heap_table_size=100; set max_join_size=100; set max_sort_length=100; set max_tmp_tables=100; set global max_user_connections=100; select @@max_user_connections; @@max_user_connections 100 set global max_write_lock_count=100; set myisam_max_extra_sort_file_size=100; select @@myisam_max_extra_sort_file_size; @@myisam_max_extra_sort_file_size 100 set myisam_max_sort_file_size=100; set myisam_sort_buffer_size=100; set net_buffer_length=100; set net_read_timeout=100; set net_write_timeout=100; set global query_cache_limit=100; set global query_cache_size=100; set global query_cache_type=demand; set read_buffer_size=100; set read_rnd_buffer_size=100; set global rpl_recovery_rank=100; set global server_id=100; set global slave_net_timeout=100; set global slow_launch_time=100; set sort_buffer_size=100; set sql_auto_is_null=1; select @@sql_auto_is_null; @@sql_auto_is_null 1 set @@sql_auto_is_null=0; select @@sql_auto_is_null; @@sql_auto_is_null 0 set sql_big_selects=1; set sql_big_tables=1; set sql_buffer_result=1; set sql_log_bin=1; set sql_log_off=1; set sql_log_update=1; set sql_low_priority_updates=1; set sql_max_join_size=200; select @@sql_max_join_size,@@max_join_size; @@sql_max_join_size @@max_join_size 200 200 set sql_quote_show_create=1; set sql_safe_updates=1; set sql_select_limit=1; set global sql_slave_skip_counter=100; set sql_warnings=1; set global table_cache=100; set table_type=myisam; set global thread_cache_size=100; set timestamp=1, timestamp=default; set tmp_table_size=100; set tx_isolation="READ-COMMITTED"; set wait_timeout=100; set log_warnings=1; create table t1 (a int not null auto_increment, primary key(a)); create table t2 (a int not null auto_increment, primary key(a)); insert into t1 values(null),(null),(null); insert into t2 values(null),(null),(null); set global key_buffer_size=100000; select @@key_buffer_size; @@key_buffer_size 98304 select * from t1 where a=2; a 2 select * from t2 where a=3; a 3 check table t1,t2; Table Op Msg_type Msg_text test.t1 check status OK test.t2 check status OK select max(a) +1, max(a) +2 into @xx,@yy from t1; drop table t1,t2;