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;
select @@VERSION=version();
@@VERSION=version()
1
select last_insert_id(345);
last_insert_id(345)
345
select @@IDENTITY,last_insert_id();
@@IDENTITY	last_insert_id()
345	345
select @@identity;
@@IDENTITY
345
select @@unknown_variable;
Unknown system variable 'unknown_variable'