结合2个SQL查询到1，从同一个表

Question

我有一个需要查询两次，产生这种格式产生结果的单一MySQL表：

+------------+----------+-------------------+ 
| Supplier | Requests | Requests_Approved | 
+------------+----------+-------------------+ 
| Supplier 1 |  50 |    45 | 
| Supplier 2 |  75 |    63 | 
| Supplier 3 |  48 |    32 | 
| Supplier 4 |  104 |    87 | 
+------------+----------+-------------------+ 

到目前为止，我已经试过如下：

SELECT Supplier, COUNT(*) AS Requests, COUNT(*) AS Requests_Approved 
FROM pricematch 
WHERE Date_Received >= '2015-01-01' 
AND Date_Received <= '2015-12-31' 
AND PM_Level = 'Escalation' 
GROUP BY Supplier 
UNION 
SELECT Supplier, COUNT(*) AS Requests, COUNT(*) AS Approved 
FROM pricematch 
WHERE Date_Time_Received >= '2015-01-01' 
AND Date_Time_Received <= '2015-12-31' 
AND PM_Level = 'Escalation' 
AND Matched = 'Yes' 
GROUP BY Supplier 
ORDER BY Requests DESC 
LIMIT 20 

哪产生以下结果表，并在两者的列数相同的结果：

+------------+----------+-------------------+ 
| Supplier | Requests | Requests_Approved | 
+------------+----------+-------------------+ 
| Supplier 1 |  50 |    50 | 
| Supplier 2 |  75 |    75 | 
| Supplier 3 |  48 |    48 | 
| Supplier 4 |  104 |    104 | 
+------------+----------+-------------------+ 

我在这里查看了很多类似的问题/答案，并尝试了使用LEFT JOIN和INNER JOIN的替代方法，但查询总是失败。

Answer 1

使用Conditional Aggregate

SELECT Supplier, 
     Count(*) AS Requests, 
     Count(CASE 
       WHEN Matched = 'Yes' THEN 1 
      END) AS Approved 
FROM pm 
WHERE Date_Received >= '2015-01-01' 
     AND Date_Received <= '2015-12-31' 
     AND PM_Level = 'Escalation' 
GROUP BY Supplier 

Answer 2

我要推测pm相同pricematch和你真的想有条件聚集：

SELECT Supplier, COUNT(*) AS Requests, 
     SUM(Matched = 'Yes') AS Approved 
FROM pricematch pm 
WHERE Date_Time_Received >= '2015-01-01' AND 
     Date_Time_Received <= '2015-12-31' AND 
     PM_Level = 'Escalation' 
GROUP BY Supplier 
ORDER BY Requests DESC 
LIMIT 20;