路径正确时，OPENJSONSQL SERVER返回null

问题描述

这是我声明的json：

DECLARE @json VARCHAR(MAX) = N'
[
 {
  "mTruckId": -35839339,"mPositionId": 68841545,"mPositionDateGmt": "laboris ipsum ullamco","mLatitude": -36598160.205007434,"mLongitude": 54707169.834195435,"mGpsValid": false,"mheading": 114,"mSpeed": -888256.4982997179,"mAdditionalinformation": {
   "mVin": "voluptate veniam","modometer": 25567959.615529776,"mEngineHours": -87509827.08880372,"mTemperatureSensors": [
    {
     "munit": "C","mLabel": "aute in","mValue": -74579140.64111689
    },{
     "munit": "C","mLabel": "ullamco labore dolore","mValue": -91870052.84894001
    }
   ]
  }
 },{
  "mTruckId": 80761376,"mPositionId": 88380593,"mPositionDateGmt": "sed pariatur ut sint","mLatitude": 62504812.42302373,"mLongitude": 14622406.17103973,"mheading": 302,"mSpeed": 39030054.634676635,"mAdditionalinformation": {
   "mVin": "aute","modometer": 74400412.05641022,"mEngineHours": 88453976.08453897,"mTemperatureSensors": [
    {
     "munit": "F","mLabel": "reprehenderit consectetur id ipsum","mValue": 22634605.53841141
    },"mLabel": "magna consectetur esse","mValue": 72633803.44269562
    }
   ]
  }
 }
]'

这是我的代码，用于从json中提取温度传感器数据。我认为这样做会成功，因为获取温度传感器数据的json层次结构是root-> mAdditionalinformation-> mTemperatureSensors。

SELECT  Unit,Label,Value
FROM OPEnjsON(@json)
WITH(
    Unit    VARCHAR(15) '$.mAdditionalinformation.mTemperatureSensors.munit',Label   VARCHAR(50) '$.mAdditionalinformation.mTemperatureSensors.mLabel',Value   FLOAT       '$.mAdditionalinformation.mTemperatureSensors.mValue'
)

它返回两行均为空的行，为什么这样做呢？我希望它能够提取mTemperatureSensors数据中的每个元素。

Unit    Label   Value
NULL    NULL    NULL
NULL    NULL    NULL

解决方法

select s.*
from openjson(@json)
with
(
    mTemperatureSensors nvarchar(max) '$.mAdditionalInformation.mTemperatureSensors' as json
) as t
cross/*outer*/ apply openjson(t.mTemperatureSensors)
with
(
mLabel nvarchar(20)
) as s

,

将 @json 的内容插入到表格中之后，一个选项是逐步应用OPENJSON到CROSS APPLY（{{ 1}}）：

tab

Demo

或根据您的情况声明标量变量 @json ：

SELECT  Unit,Label,Value
  FROM tab
 CROSS APPLY OPENJSON(JsonData)
             WITH (
                    TempSens NVARCHAR(MAX) '$.mAdditionalInformation.mTemperatureSensors' AS JSON ) Q1 
 CROSS APPLY OPENJSON (Q1.TempSens) 
             WITH (
                    Unit   NVARCHAR(MAX) '$.mUnit',Label  NVARCHAR(MAX) '$.mLabel',Value  FLOAT         '$.mValue'
                  ) Q2    

Demo