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drop table if exists t1,t2;
set @a := foo;
ERROR 42S22: Unknown column 'foo' in 'field list'
set @a := connection_id() + 3;
select @a - connection_id();
@a - connection_id()
3
set @b := 1;
select @b;
@b
1
CREATE TABLE t1 ( i int not null, v int not null,index (i));
insert into t1 values (1,1),(1,3),(2,1);
create table t2 (i int not null, unique (i));
insert into t2 select distinct i from t1;
select * from t2;
i
1
2
select distinct t2.i,@vv1:=if(sv1.i,1,0),@vv2:=if(sv2.i,1,0),@vv3:=if(sv3.i,1,0), @vv1+@vv2+@vv3 from t2 left join t1 as sv1 on sv1.i=t2.i and sv1.v=1 left join t1 as sv2 on sv2.i=t2.i and sv2.v=2 left join t1 as sv3 on sv3.i=t2.i and sv3.v=3;
i @vv1:=if(sv1.i,1,0) @vv2:=if(sv2.i,1,0) @vv3:=if(sv3.i,1,0) @vv1+@vv2+@vv3
1 1 0 1 2
2 1 0 0 1
explain select * from t1 where i=@vv1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref i i 4 const 1 Using where
explain select * from t1 where @vv1:=@vv1+1 and i=@vv1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ALL NULL NULL NULL NULL 3 Using where
explain select @vv1:=i from t1 where i=@vv1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 index NULL i 4 NULL 3 Using where; Using index
explain select * from t1 where i=@vv1;
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE t1 ref i i 4 const 1 Using where
drop table t1,t2;
set @a=0,@b=0;
select @a:=10, @b:=1, @a > @b, @a < @b;
@a:=10 @b:=1 @a > @b @a < @b
10 1 1 0
select @a:="10", @b:="1", @a > @b, @a < @b;
@a:="10" @b:="1" @a > @b @a < @b
10 1 1 0
select @a:=10, @b:=2, @a > @b, @a < @b;
@a:=10 @b:=2 @a > @b @a < @b
10 2 0 1
select @a:="10", @b:="2", @a > @b, @a < @b;
@a:="10" @b:="2" @a > @b @a < @b
10 2 1 0
select @a:=1;
@a:=1
1
select @a, @a:=1;
@a @a:=1
1 1
create table t1 (id int, d double, c char(10));
insert into t1 values (1,2.0, "test");
select @c:=0;
@c:=0
0
update t1 SET id=(@c:=@c+1);
select @c;
@c
1
select @c:=0;
@c:=0
0
update t1 set id=(@c:=@c+1);
select @c;
@c
1
select @c:=0;
@c:=0
0
select @c:=@c+1;
@c:=@c+1
1
select @d,(@d:=id),@d from t1;
@d (@d:=id) @d
NULL 1 1
select @e,(@e:=d),@e from t1;
@e (@e:=d) @e
NULL 2 2
select @f,(@f:=c),@f from t1;
@f (@f:=c) @f
NULL test test
set @g=1;
select @g,(@g:=c),@g from t1;
@g (@g:=c) @g
1 test test
select @c, @d, @e, @f;
@c @d @e @f
1 1 2 test
select @d:=id, @e:=id, @f:=id, @g:=@id from t1;
@d:=id @e:=id @f:=id @g:=@id
1 1 1 NULL
select @c, @d, @e, @f, @g;
@c @d @e @f @g
1 1 1 1 NULL
drop table t1;
select @a:=10, @b:=2, @a>@b, @a:="10", @b:="2", @a>@b, @a:=10, @b:=2, @a>@b, @a:="10", @b:="2", @a>@b;
@a:=10 @b:=2 @a>@b @a:="10" @b:="2" @a>@b @a:=10 @b:=2 @a>@b @a:="10" @b:="2" @a>@b
10 2 1 10 2 1 10 2 1 10 2 1
create table t1 (i int not null);
insert t1 values (1),(2),(2),(3),(3),(3);
select @a:=0;
@a:=0
0
select @a, @a:=@a+count(*), count(*), @a from t1 group by i;
@a @a:=@a+count(*) count(*) @a
0 1 1 0
0 2 2 0
0 3 3 0
select @a:=0;
@a:=0
0
select @a+0, @a:=@a+0+count(*), count(*), @a+0 from t1 group by i;
@a+0 @a:=@a+0+count(*) count(*) @a+0
0 1 1 0
1 3 2 0
3 6 3 0
drop table t1;
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