Question

我有a次竞价和b次竞价：

表a（拍卖）：

id status
1    1
2    0
3    0
4    1

表b（投标）：

id  auction_id   amount    date
1       1          0.1   2018-01-24
2       1          0.1   2018-01-24
3       4          0.2   2018-01-26
4       4          0.1   2018-01-26
5       4          0.3   2018-01-28
6       1          0.1   2018-01-29

我想得到的是出价金额，出价总额，每个竞价的最后出价日期b以及表格a中所有内容的ID和状态状态：

这样的事情：

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，我有这个问题：

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个出价的拍卖

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

我需要所有拍卖。你能帮忙吗？谢谢！

Answer 1

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

Answer 2

您要做的是left join：

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

mysql使用JOIN从2个表中获取拍卖数据和出价

2 个答案: