SQL Server – make a copy of parent child rows

Let us say we have 2 tables that are in a parent-child relation.

We want to make a copy of the FormSectionInstance rows, but also copy and correlate the FormDetails rows.

This means copy rows from 2 tables and then set them up with the correct NEW corresponding IDs.

We could use a cursor, but a better alternative is the the MERGE INTO function.

We also create a TEMP transition table to hold the new VS old values. We use these values when we insert the CHILD values.

This way we can make the INSERT faster.

-- Copy the FormSectionInstance
DECLARE @FormSectionInstanceTable TABLE(OldFormSectionInstanceId INT, NewFormSectionInstanceId INT)

;MERGE INTO [dbo].[FormSectionInstance]
USING
(
	SELECT
		fsi.FormSectionInstanceId [OldFormSectionInstanceId]
		, @NewFormHeaderId [NewFormHeaderId]
		, fsi.FormSectionId
		, fsi.IsClone
		, @UserId [NewCreatedByUserId]
		, GETDATE() NewCreatedDate
		, @UserId [NewUpdatedByUserId]
		, GETDATE() NewUpdatedDate
	FROM [dbo].[FormSectionInstance] fsi
	WHERE fsi.[FormHeaderId] = @FormHeaderId 
) tblSource ON 1=0 -- use always false condition
WHEN NOT MATCHED
THEN INSERT
( [FormHeaderId], FormSectionId, IsClone, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
VALUES( [NewFormHeaderId], FormSectionId, IsClone, NewCreatedByUserId, NewCreatedDate, NewUpdatedByUserId, NewUpdatedDate)
	
OUTPUT tblSource.[OldFormSectionInstanceId], INSERTED.FormSectionInstanceId
INTO @FormSectionInstanceTable(OldFormSectionInstanceId, NewFormSectionInstanceId);
	

-- Copy the FormDetail
INSERT INTO [dbo].[FormDetail]
	(FormHeaderId, FormFieldId, FormSectionInstanceId, IsOther, Value, CreatedByUserId, CreatedDate, UpdatedByUserId, UpdatedDate)
SELECT
	@NewFormHeaderId, FormFieldId, fsit.NewFormSectionInstanceId, IsOther, Value, @UserId, CreatedDate, @UserId, UpdatedDate
FROM [dbo].[FormDetail] fd
INNER JOIN @FormSectionInstanceTable fsit ON fsit.OldFormSectionInstanceId = fd.FormSectionInstanceId
WHERE [FormHeaderId] = @FormHeaderId 

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