mysql使用JOIN从2个表中获取拍卖数据和出价

我有表

a

拍卖和表

b

出价：

表

a

（拍卖）：

表

b

（投标文件）：

我想要得到的是表

b

中的出价金额、总出价、每次拍卖的最后出价日期，以及表

a

中的id和状态，所有按状态排序的物品：

大概是这样的：

id  status  bid_sum  bid_count  last_bid_date
4     1       0.6       3         2018-01-28
1     1       0.3       3         2018-01-29
3     0        0        0         0000-00-00
2     0        0        0         0000-00-00

到目前为止，我有一个疑问：

SELECT a.id, a.status, SUM( b.amount ) as bids_sum, COUNT( b.id ) as bids_count, MAX( b.dt ) as last_bid_date 
FROM a, b 
GROUP BY a.id 
ORDER BY a.status DESC, a.id DESC

问题是，它只返回至少有1次出价的拍卖

id  status  bid_sum  bid_count  last_bid_date
4     1       0.6       3         2018-01-28
1     1       0.3       3         2018-01-29

---

我需要所有的拍卖。你能帮忙吗？谢谢大家!

您要做的是

左连接

：

SELECT a.id,
       a.status,
       SUM(b.amount) AS bids_sum,
       COUNT(b.id) AS bids_count,
       MAX(b.dt) AS last_bid_date
FROM a
LEFT JOIN b ON a.id = b.auction_id
GROUP BY a.id
ORDER BY a.status DESC,
         a.id DESC

---

使用适当的

连接
。它已经存在20多年了。
id  status  bid_sum  bid_count  last_bid_date
4     1       0.6       3         2018-01-28
1     1       0.3       3         2018-01-29

SELECT a.id,
       a.status,
       SUM(b.amount) AS bids_sum,
       COUNT(b.id) AS bids_count,
       MAX(b.dt) AS last_bid_date
FROM a
LEFT JOIN b ON a.id = b.auction_id
GROUP BY a.id
ORDER BY a.status DESC,
         a.id DESC

SELECT 
    a.id, 
    a.status, 
    COALESCE(SUM(b.amount), 0) as bids_sum, 
    COUNT(b.id) as bids_count, 
    COALESCE(MAX(b.dt), '0000-00-00') as last_bid_date 
FROM a left outer join b 
  on a.id = b.auction_id 
GROUP BY a.id 
ORDER BY a.status DESC, a.id DESC