"折叠"表以消除空值

Question

我有一个产品,允许在GUI中创建自定义字段.我创建了三个字段:系统发货日期,系统保修结束日期和系统保修说明.遗憾的是,系统将这些填充为行而不是列.

例:

Machine_GroupID      | agentGuid | fieldName                |  fieldValue
-----------------------------------------------------------------------------
systemABC.companyABC | 57537921  | System Ship Date         | 1/1/1900
systemABC.companyABC | 57537921  | System Warranty End Date | 1/1/1950
systemABC.companyABC | 57537921  | System Warranty Notes    | Test notes
system123.companyABC | 48394844  | System Ship Date         | 1/1/1900
system123.companyABC | 48394844  | System Warranty End Date | 1/1/1950
system123.companyABC | 48394844  | System Warranty Notes    | Test notes
systemXYZ.companyABC | 99948403  | System Ship Date         | 1/1/1900
systemXYZ.companyABC | 99948403  | System Warranty End Date | 1/1/1950
systemXYZ.companyABC | 99948403  | System Warranty Notes    | Test notes

我需要将系统发货日期作为列,系统保修结束日期作为列,将系统保修说明作为列返回.如果我使用CASE WHEN语句:

CASE WHEN sim.fieldName = 'System Ship Date' 
     THEN sim.fieldValue END AS 'System Ship Date',
CASE WHEN sim.fieldName = 'System Warranty End Date' 
     THEN sim.fieldValue END AS 'System Warranty End Date',
CASE WHEN sim.fieldName = 'System Warranty Notes' 
     THEN sim.fieldValue END AS 'System Warranty Notes'

因此,数据显示在每台计算机上:

header1 header2 header3
data1 NULL NULL
NULL data2 NULL
NULL NULL data3

我需要它看起来像这样:

header1 header2 header3
data1 data2 data3

我以为我可以以某种方式使用MAX(),但我是一个新手而且它超出了我.或者我知道我可以创建一个临时表,但我也不知道.我已经在网上和堆栈上进行了广泛的搜索,但是我能得到的就是CASE WHEN语句.

Answer 1

为什么不加入SELF？保持简单......

SELECT
   s1.Machine_GroupID, s1.agentGuid,
   s1.fieldValue, s2.fieldValue, s3.fieldValue
FROM
   sim s1
   JOIN sim s2 ON s1.Machine_GroupID = s2.Machine_GroupID
   JOIN sim s3 ON s1.Machine_GroupID = s3. Machine_GroupID
WHERE
   s1.fieldName = 'System Ship Date' AND
   s2.fieldName = 'System Warranty End Date' AND
   s2.fieldName = 'System Warranty Notes'

Answer 2

在MS SQL中:

SELECT
  Machine_GroupID, agentGuid, "System Ship Date", "System Warranty End Date", "System Warranty Notes"
FROM
  (
  SELECT
    Machine_GroupID, agentGuid, fieldName, MAX(fieldValue) AS Value
  FROM
    sim
  GROUP BY
    Machine_GroupID, agentGuid, fieldName
  ) AS X
PIVOT
  (MAX(Value) FOR fieldName IN ("System Ship Date", "System Warranty End Date", "System Warranty Notes")) AS Y

GROUP BY在您的情况下,该子句并不是绝对必要的,但没有它PIVOT有时会返回无关的行,而不是像您的第一个表.