q15

SET @rowid=0;
SET @cnt=(SELECT COUNT(*) FROM good);
SET @middle_no=CEIL(@cnt/2);
SET @odd_even=NULL;

SELECT AVG(price) AS median
FROM (SELECT
price,
@rowid:=@rowid+1 AS rid,
(CASE WHEN(MOD(@cnt,2)=0) THEN @odd_even:=1 ELSE @odd_even:=0 END) AS odd_even_status
FROM good
ORDER BY price) AS tbl
WHERE
tbl.rid=@middle_no
OR
tbl.rid=(@middle_no+@odd_even);