SQL – INNER vs Left

Select sah.*,ari.*
From prddtalib.slsah sah
Inner join prddtalib.arari ari on ari.UCIHACTID = sah.actid
left join prddtalib.slsad sad on sad.actid=ari.UCITACTID
Where sad.sahnum is null

vs

SELECT * FROM devdtalib/slsah, devdtalib/arari WHERE SLSAH.ACTID =
ARARI.UCIHACTID and NOT EXISTs( SELECT SLSAD.ACTID FROM
DEVDTALIB/SLSAD where ARARI.UCITACTID = SLSAD.ACTID)