Resolve MERGE Statement issue on CDC Enabled Table

This will happen only when the table has a unique clustered\non-clustered index on it. CDC[Change Data Capture] is a tool to handle change tracking on SQL Server 2008 or above, it logs all inserts\updates\deletes on a table. When you fire a MERGE statement that will update a record, it will log the change in CDC table as DELETE followed by INSERT. The expected result is an UPDATE. Let’s understand it with an example.

Create a table with unique nonclustered index using below script:

  1. USE[EmployeeeDB]  
  3. CREATETABLE[dbo].[Table1]  
  4. (  
  5. [AppraisalNumber][nvarchar](40)NOTNULL  
  6. )  
  7. CREATEUNIQUENONCLUSTEREDINDEX[NonClusteredIndex-20160303-155449]ON[dbo].[Table1]  
  8. (  
  9. [AppraisalNumber]ASC  
  11. GO  
  13. Enable CDC on EmployeeDB using:  
  15. EXECsys.sp_cdc_enable_db;  
Enable CDC on Table1 using:
  1. EXECsys.sp_cdc_enable_table@source_schema=N'dbo',@source_name='Table1',@role_name=N'cdc_admin'  
Execute below MERGE statement to do an update on Table1:


If you check CDC table, it will show DELETE [__$operation as 1] followed by INSERT [__$operation as 2] for a UPDATE operation using MERGE statement:


To resolve it, we need to add startup parameter -T8207 to SQL Server instance by following below steps:

Open SQL Server configuration Manager:


Select your instance and go to properties -> Startup parameters tab -> Add -T8207 than click Add and restart the instance.


Now, execute the same MERGE statement and check CDC table:


We will see Update before [__$operation=3] and Update After[__$operation=4]. For more details, please refer here.

I am ending things here, I hope this article will be helpful for all.


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