How Dynamicaly columns in UNPIVOT operator - tsql

Question

I currently have the following query:
WITH History AS (
SELECT
kz.*,
kz.__$operation AS operation,
map.tran_begin_time as beginT,
map.tran_end_time as endT
FROM cdc.fn_cdc_get_all_changes_dbo_EXT_GeolObject_KategZalezh(sys.fn_cdc_get_min_lsn('dbo_EXT_GeolObject_KategZalezh'), sys.fn_cdc_get_max_lsn(), 'all') AS kz
INNER JOIN [cdc].[lsn_time_mapping] map
ON kz.[__$start_lsn] = map.start_lsn
where kz.GUID_BalanceHC_Zalezh = 'DDA9AB3A-A0AF-4623-9362-0000C8C83D63'
),
UnpivotedValues AS(
SELECT guid, GUID_another, field, val, operation, beginT, endT
FROM History
UNPIVOT ( [val] FOR field IN
(
area,
oilwidthmin,
oilwidthmax,
efectivwidthmin,
efectivwidthmax,
etc...
))t
),
UnpivotedWithLastValue AS (
SELECT
*,
--Use LAG() to get the last value for the same field
LAG(val, 1) OVER (PARTITION BY guid, GUID_another, field ORDER BY BeginT) LastVal
FROM UnpivotedValues
)
SELECT * FROM UnpivotedWithLastValue WHERE val <> LastVal OR LastVal IS NULL ORDER BY guid
This query returns the changed values for a single table that has CDC (Change Data Capture) enabled.
I want to create a stored procedure that receives the columns to be unpivoted, and the cdc function (e.g. cdc.fn_cdc_get_all_...) as parameters and returns the result set.
The result for this tables must be joined in one report.
In my case parameter 1 is cdc.fn_cdc_get_all_changes_dbo_EXT_GeolObject_KategZalezh(sys.fn_cdc_get_min_lsn('dbo_EXT_GeolObject_KategZalezh'), sys.fn_cdc_get_max_lsn(), 'all'). This is the CDC function.
How should I send the list of fields that i want in the result? How's the string?
Also, is there a way to do without dynamic SQL? Dynamic SQL it is not better solution for performance.

Answer 1

As you know SQL Server is declarative by design and does not support macro substitution.
UNPIVOT would clearly be more performant, but here is a simplified example of a UNPIVOT which does not require Dynamic SQL, but only a little XML.
Example
Let's assume your table/results looks like this:
You may notice that I only we only specify key fields to EXCLUDE in the final WHERE
Declare #YourData table (ID int,Active bit,First_Name varchar(50),Last_Name varchar(50),EMail varchar(50),Salary decimal(10,2))
Insert into #YourData values
(1,1,'John','Smith','john.smith#email.com',85600),
(2,0,'Jane','Doe' ,'jane.doe#email.com',83200)
;with cte as (
-- Replace with your Complex Query
Select * from #YourData
)
Select A.ID
,A.Active
,C.*
From cte A
Cross Apply (Select XMLData=cast((Select A.* for XML RAW) as xml)) B
Cross Apply (
Select Item = attr.value('local-name(.)','varchar(100)')
,Value = attr.value('.','varchar(max)')
From XMLData.nodes('/row') C1(n)
Cross Apply C1.n.nodes('./#*') C2(attr)
Where attr.value('local-name(.)','varchar(100)') not in ('ID','Active')
) C
Returns