从一行中选择两个不同的值

Question

我想要这张桌子

预订表

+----+--------+
| ID | Status |
+----+--------+
| 1  | R      |
| 2  | R      |
| 3  | C      |
| 4  | C      |
+----+--------+

每个

的总数

+----------+-----------+
| Reserved | Cancelled |
+----------+-----------+
| 2        | 2         |
+----------+-----------+

到目前为止，我得到了这个 -

SELECT Status AS Reserves 
FROM Booking WHERE Status = 'R' OR Status = 'C'

输出 -

+----------+
| reserves |
+----------+
| R        |
| C        |
| R        |
| C        |
+----------+

Answer 1

将WHERE子句中的逻辑放入CASE表达式中，并将其加到整个表中：

SELECT
    SUM(CASE WHEN Status = 'R' THEN 1 END) AS Reserved,
    SUM(CASE WHEN Status = 'S' THEN 1 END) AS Cancelled
FROM Booking