sql从索引中选择行

Question

if i had 10 rows which fits this description on mysql

SELECT id, nav, img 
FROM mytable 
WHERE id='$id' 
ORDER BY pageDisplayNum ASC;

pageDisplayNum may not be in numeric order, meaning 1, 2, 5, 10, 16, 22 etc...
q: how can i choose the 3rd or 6th item from this list

the index number would be coming in from php as a variable
i read about TOP but this didnt work either

SELECT TOP $num 
id, nav, img 
FROM mytable 
WHERE id='$id'
ORDER BY pageDisplayNum ASC;

Answer 1

This for 7th item

SELECT id, nav, img 
FROM mytable 
WHERE id='$id' 
ORDER BY pageDisplayNum ASC;
LIMIT 6,1

You can add LIMIT offset,row_count query