>What's the main difference of those 2 SQLs? Am I right to say that the first one is faster than the second one?
>
>SELECT ELEM_ID FROM ELEM WHERE EXISTS (SELECT ELEM_ID FROM ANSWER WHERE RATER_ID=254 AND ANSWER.ELEM_ID=ELEM.ELEM_ID)
>
>SELECT ELEM.ELEM_ID FROM ELEM,ANSWER WHERE ANSWER.RATER_ID=254 AND ANSWER.ELEM_ID=ELEM.ELEM_ID AND ELEM.CHILDREN

where is the elem.children in the first sql?

in theory (according to the books) the first one should be faster...