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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'
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