-- Create temporary tables

create table tmp1 (idTmp1 int unsigned not null primary key);

create table tmp2 (idTmp2 int unsigned not null primary key,

  idTmp1 int unsigned not null,

  vlr decimal(12,2),

  foreign key (idTmp1) references tmp1(idTmp1));

-- Insert some data

insert into tmp1 values (1);

-- without where works as expected

select tmp1.idTmp1, tmp2.idTmp2, sum(tmp2.vlr)

from tmp1

inner join tmp2 on tmp2.idTmp1=tmp1.idTmp1;

-- returns Null, Null, Null

-- with an equality condition in tmp1 brings unexpected data in first field

select tmp1.idTmp1, tmp2.idTmp2, sum(tmp2.vlr)

from tmp1

inner join tmp2 on tmp2.idTmp1=tmp1.idTmp1

where tmp1.idTmp1=1;

-- returns 1, Null, Null

-- with a range (simulating equality) in tmp1 brings unexpected data in first field

select tmp1.idTmp1, tmp2.idTmp2, sum(tmp2.vlr)

from tmp1

inner join tmp2 on tmp2.idTmp1=tmp1.idTmp1

where tmp1.idTmp1 between 1 and 1;

-- returns 1, Null, Null

-- with an range (different range) in tmp1 works as expected

select tmp1.idTmp1, tmp2.idTmp2, sum(tmp2.vlr)

from tmp1

inner join tmp2 on tmp2.idTmp1=tmp1.idTmp1

where tmp1.idTmp1 between 0 and 2;

-- returns Null, Null, Null