Add cdc_readme.md

cdc_readme.md

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+
+-- CDC
+-- Step 1: Check SQL Server Agent  
+-- Step 2:Enable CDC at Database Level
+
+Query - EXEC sys.sp_cdc_enable_db;
+
+--Verify CDC enabled for database
+
+SELECT name,is_cdc_enabled
+FROM sys.databases
+WHERE name = 'YourDatabaseName';
+
+--if is_cdc_enabled = 1, CDC is enabled.
+
+--Step 3: Enable CDC for a Table
+
+EXEC sys.sp_cdc_enable_table
+    @source_schema = 'dbo',
+    @source_name   = 'Employee',
+    @role_name     = NULL;
+
+-- Step 4: Verify CDC Enabled for Table
+SELECT name,is_tracked_by_cdc
+FROM sys.tables
+WHERE name = 'Employee';
+
+--Step 5: Check CDC Tables
+
+SELECT *
+FROM cdc.change_tables;
+--You may see: 'cdc.dbo_Employee_CT'
+
+-- Step 6: Test CDC
+Insert,Update,Delete
+
+--Step 7: Read CDC Data
+SELECT * FROM cdc.dbo_Employee_CT;
+
+Step 8: Disable CDC (Optional)
+
+EXEC sys.sp_cdc_disable_table
+    @source_schema = 'dbo',
+    @source_name   = 'Employee',
+    @capture_instance = 'dbo_Employee';
+
+-- Disable database CDC
+EXEC sys.sp_cdc_disable_db;
+
+-- Important Notes
+CDC is available in:
+SQL Server Enterprise
+Standard Edition (SQL Server 2016 SP1 and later)
+Table must have a:
+Primary Key (recommended)
+Or unique index
+SQL Server Agent must remain running
+
+Architecture Overview
+Table Changes
+      ↓
+Transaction Log
+      ↓
+CDC Capture Job
+      ↓
+cdc.<table>_CT Table
+      ↓
+Query CDC Data
+
+