[英]How do I get the MAX date of foreign table in MySQL and return only the row with that data without mixing records?
我有一些MySQL表,我需要從中加入並返回數據。 返回數據必須只為其中一個JOINed表顯示一行,但MySQL會混合這些行。
我嘗試過使用子查詢的不同方法和使用GROUP的常規JOIN,但結果幾乎保持不變。
示例表結構
suppliers
id name ...
1 ACME ...
2 EMCA ...
3 ORG ...`
ratings
id supplier_id rating expiry_date report_file
1 1 5.0 2017-01-31 a.pdf
3 1 7.9 2019-06-30 c.pdf
4 2 5.0 2016-01-31 d.pdf
5 2 2.0 2018-11-30 g.pdf
6 245 9.5 2009-03-31 p.pdf
spends
id report_id supplier_id amount
1 1 1 150.00
2 1 2 100.00
3 1 245 200.00
以下是我嘗試解決此問題並返回正確數據集但沒有運氣的示例查詢。
SELECT
reports.id,
suppliers.id AS supplier_id,
suppliers.name,
...
spends.amount,
...
ratings.rating,
ratings.report_file,
ratings.expiry_date
FROM reports
INNER JOIN spends ON reports.id=spends.report_id
INNER JOIN suppliers ON spends.supplier_id=suppliers.id
LEFT JOIN (
SELECT id,
level,
report_file,
supplier_id,
MAX(expiry_date) AS expiry_date
FROM ratings
GROUP BY supplier_id
) ratings ON (ratings.supplier_id=suppliers.id
AND ratings.expiry_date >= reports.period_start)
...
WHERE reports.id = 1
GROUP BY spends.id
ORDER BY spends.amount DESC
另一個問題
SELECT
reports.id,
suppliers.id AS supplier_id,
suppliers.name,
...
spends.amount,
...
ratings.rating,
ratings.report_file,
MAX(ratings.expiry_date) AS expiry_date
FROM reports
INNER JOIN spends ON reports.id=spends.report_id
INNER JOIN suppliers ON spends.supplier_id=suppliers.id
LEFT JOIN ratings ON (ratings.supplier_id=suppliers.id
AND ratings.expiry_date >= reports.period_start)
...
WHERE reports.id = 1
GROUP BY spends.id
ORDER BY spends.amount DESC
我期待結果
id supplier_id name amount rating report_file expiry_date
1 1 ACME 150.00 7.9 c.pdf 2019-06-30
1 2 EMCA 100.00 2.0 g.pf 2018-11-30
1 245 MACE 200.00 null null```
However, the actual output is
```sql
id supplier_id name amount rating report_file expiry_date
1 1 ACME 150.00 5.0 a.pdf 2019-06-30
1 2 EMCA 100.00 5.0 d.pf 2018-11-30
1 245 MACE 200.00 null null
請任何人都可以告訴我如何解決這個問題。
嘗試這樣的查詢:
SELECT
reports.id,
suppliers.id AS supplier_id,
suppliers.name,
...
spends.amount,
...
r.rating,
r.report_file,
r.expiry_date
FROM reports
INNER JOIN spends ON reports.id=spends.report_id
INNER JOIN suppliers ON spends.supplier_id=suppliers.id
LEFT JOIN ratings r ON r.supplier_id=suppliers.id
AND r.`expire_date` = (
SELECT MAX(`expire_date`) FROM ratings WHERE supplier_id = supplier.id GROUP BY supplier_id)
) as maxdate
...
WHERE reports.id = 1
GROUP BY spends.id
ORDER BY spends.amount DESC
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