Now I wonder which way would be efficiecier as follow:
1.
select tisfc001.mitm, tisfc001.osta, tisfc927.clot
from tisfc001, tisfc927
where tisfc001._index1 = {:tiitm926.pdno}
and tisfc927._index2 = {:tiitm926.pdno}

2.
select tisfc001.mitm, tisfc001.osta, tisfc927.clot
from tisfc001, tisfc927
where tisfc927._index2 = {:tiitm926.pdno}
and tiitm926.pdno refers to tisfc001

Moderns database use to improve the query automatically.
It receive the query and optimize it to improve the performance.
You can check it with your DBA for this db functionality