mysql - 将同一个表中的 2 个 SQL 查询合并为 1 个

Question

我有一个 MySQL 表，需要查询两次才能生成以下格式的结果:

+------------+----------+-------------------+
|  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，我已经尝试过以下方法:

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

这会产生以下结果表，两个数字列中的结果相同:

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

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

Answer 1

使用条件聚合

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