SQL选择里面选择

Question

I have 3 tables.

person{personid,name, etc}
bid{bidid,personid,etc}
rating{ratingid,bidid,rating}

A person gets the rating after the bid is accepted by customers. So 1 bid = 1 rating . And then the person bids another order, but the rating won't show up.

I already tried:

SELECT a.namausaha,ROUND(AVG(c.rating)) AS rating,a.kota,a.kontak,b.bidprice,a.mitraid
FROM tb_mitra a
JOIN tb_bid b ON b.mitraid=a.mitraid
LEFT JOIN tb_rating c ON c.bidid=b.bidid
WHERE b.orderid='OD004' AND b.statusbidid='1'
GROUP BY a.mitraid  

but it doesn't work.

How to do it? I want to show the rating for every person.

Answer 1

Some rating return null due to left join

Try this

SELECT a.name,
  ROUND(AVG(CASE WHEN c.rating IS NULL THEN 1 ELSE c.rating END )) AS rating,
  a.etc,b.etc,a.personid
FROM person a
JOIN bid b ON b.personid=a.personid
LEFT JOIN rating c ON c.bidid=b.bidid
GROUP BY a.personid 

SQL Fiddle