Question

样本数据：

表：PollingSettings

示例行：

ID | Frequency      | Value
---+----------------+-------
 1 | Frequency      | 300
 1 | Timeout        | 500
 2 | Frequency      | 1200
 2 | Timeout        | 100
 3 | LogFilesToKeep | 30
 3 | DebugEnabled   | False

我需要一条select语句，该语句将执行以下操作：

 SELECT ID, key as Frequency, key as Timeout

 CASE Freqency
      WHEN Frequency = 'Frequency' THEN value
 CASE Timeout
      WHEN Timeout = 'Timeout' THEN value
 END
 FROM PollingSettings

基本上，我需要创建两个名为timeout和frequency的新列，但前提是ID具有一个键值为“ frequency”或“ timeout”的键列，并将该列称为“ frequency”或“ timeout”与键值对中的值。否则，仍应创建这些列，而应将它们设置为“ null”。最终结果是这样的：

ID | Frequency   | Timeout
---+-------------+-------
 1 | 300         | 500
 2 | 1200        | 100

Answer 1

您只需要创建两个包含case语句的列并获取最大值，这样每个ID仅获得1行：

select ID, 
    max(case when key='Frequency' then value end) as Frequency,
    max(case when key='Timeout' then value end) as Timeout
from PollingSettings
group by ID

Answer 2

请与CASE WHEN一起尝试：

SELECT ID, min(CASE WHEN key = 'Frequency' THEN value end) as Frequency,
 min(CASE WHEN key = 'Timeout' THEN value end) as Timeout
 FROM PollingSettings group by ID

SQL Select语句（如果列与值匹配）作为ColumnName

2 个答案: