drop table if exists t1;
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 GLOBAL myisam_max_sort_file_size=2000000;
show global variables like 'myisam_max_sort_file_size';
Variable_name	Value
myisam_max_sort_file_size	1048576
set GLOBAL myisam_max_sort_file_size=default;
show variables like 'myisam_max_sort_file_size';
Variable_name	Value
myisam_max_sort_file_size	FILE_SIZE
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 "convert_character_set";
Variable_name	Value
convert_character_set	cp1251_koi8
set character set cp1251_koi8;
show variables like "convert_character_set";
Variable_name	Value
convert_character_set	cp1251_koi8
set global character set default, session character set default;
show variables like "convert_character_set";
Variable_name	Value
convert_character_set	cp1251_koi8
select @@timestamp>0;
@@timestamp>0
1
set @@rand_seed1=10000000,@@rand_seed2=1000000;
select ROUND(RAND(),5);
ROUND(RAND(),5)
0.02887
show variables like '%alloc%';
Variable_name	Value
query_alloc_block_size	8192
query_prealloc_size	8192
range_alloc_block_size	2048
transaction_alloc_block_size	8192
transaction_prealloc_size	4096
set @@range_alloc_block_size=1024*16;
set @@query_alloc_block_size=1024*17+2;
set @@query_prealloc_size=1024*18;
set @@transaction_alloc_block_size=1024*20-1;
set @@transaction_prealloc_size=1024*21-1;
select @@query_alloc_block_size;
@@query_alloc_block_size
17408
show variables like '%alloc%';
Variable_name	Value
query_alloc_block_size	17408
query_prealloc_size	18432
range_alloc_block_size	16384
transaction_alloc_block_size	19456
transaction_prealloc_size	20480
set @@range_alloc_block_size=default;
set @@query_alloc_block_size=default, @@query_prealloc_size=default;
set transaction_alloc_block_size=default, @@transaction_prealloc_size=default;
show variables like '%alloc%';
Variable_name	Value
query_alloc_block_size	8192
query_prealloc_size	8192
range_alloc_block_size	2048
transaction_alloc_block_size	8192
transaction_prealloc_size	4096
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 convert_character_set=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 'convert_character_set'
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
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
set myisam_max_sort_file_size=100;
Variable 'myisam_max_sort_file_size' is a GLOBAL variable and should be set with SET GLOBAL
set myisam_max_extra_sort_file_size=100;
Variable 'myisam_max_extra_sort_file_size' is a GLOBAL variable and should be set with SET GLOBAL
set @@SQL_WARNINGS=NULL;
Variable 'sql_warnings' can't be set to the value of 'NULL'
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 convert_character_set=cp1251_koi8;
set convert_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 global myisam_max_extra_sort_file_size=100;
select @@myisam_max_extra_sort_file_size;
@@myisam_max_extra_sort_file_size
100
set global 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;
DROP TABLE IF EXISTS t1,t2;
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
drop table t1,t2;
select @@xxxxxxxxxx;
Unknown system variable 'xxxxxxxxxx'
select 1;
1
1
select @@session.key_buffer_size;
Variable 'key_buffer_size' is a GLOBAL variable
set global myisam_max_sort_file_size=4294967296;
show global variables like 'myisam_max_sort_file_size';
Variable_name	Value
myisam_max_sort_file_size	MAX_FILE_SIZE
set @tstlw = @@log_warnings;
show global variables like 'log_warnings';
Variable_name	Value
log_warnings	1
set global log_warnings = 0;
show global variables like 'log_warnings';
Variable_name	Value
log_warnings	0
set global log_warnings = 42;
show global variables like 'log_warnings';
Variable_name	Value
log_warnings	42
set global log_warnings = @tstlw;
show global variables like 'log_warnings';
Variable_name	Value
log_warnings	1