In sqlite

here is the tables:

create table users ( email char(20), name char(16), pwd char(4), city char(15), gender char(1), primary key (email) ); create table products ( pid char(4), descr char(20), primary key (pid) ); create table sales ( sid char(4), lister char(20) not null, pid char(4), edate date, descr char(25), cond char(10), rprice int, primary key (sid), foreign key (lister) references users, foreign key (pid) references products ); create table bids ( bid char(20), bidder char(20) not null, sid char(4) not null, bdate date, amount float, primary key (bid), foreign key (bidder) references users, foreign key (sid) references sales ); create table items ( sid char(4), no int, pid char(4), descr char(25), primary key (sid,no), foreign key (sid) references sales on delete cascade, foreign key (pid) references products ); create table reviews ( reviewer char(20), reviewee char(20), rating float, rtext char(20), rdate date, primary key (reviewer, reviewee), foreign key (reviewer) references users, foreign key (reviewee) references users ); create table previews ( rid int, pid char(4), reviewer char(20) not null, rating float, rtext char(20), rdate date, primary key (rid), foreign key (pid) references products, foreign key (reviewer) references users ); create table endorses ( rid int, endorser char(20), primary key (rid, endorser), foreign key (rid) references previews, foreign key (endorser) references users );

This is the question:

Find all undervalued sales that have the term xbox in their descriptions; a sale s is undervalued if it is associated to a product p and p is associated with another sale s' and the highest bid for s' is more than twice the amount of the highest bid for s. Matching of the keyword xbox must be case-insensitive. For each qualifying sale s, list sid, lister of the sale, pid of the product associated with the sale and the maximum bid amount offered for the sale.

I worked on it i got this but doesn't work please help:

select sales.sid, sales.lister, sales.pid, MAX(bids.amount) as max_bid from sales left join bids on sales.sid = bids.sid where sales.descr like '%xbox%' group by sales.pid, sales.sid, sales.lister having 2 * bids.amount >= MAX(bids.amount);