[GitHub] [carbondata] ajantha-bhat commented on a change in pull request #3754: [CARBONDATA-3808] Added documentation for cdc and scd scenarios

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ajantha-bhat commented on a change in pull request #3754:
URL: https://github.com/apache/carbondata/pull/3754#discussion_r421943365



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File path: docs/scd-and-cdc-guide.md
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+
+# Upsert into a Carbon DataSet using Merge 
+
+## SCD and CDC Scenarios
+Change Data Capture (CDC), is to apply all data changes generated from an external data set 
+into a target dataset. In other words, a set of changes (update/delete/insert) applied to an external 
+table needs to be applied to a target table.
+
+Slowly Changing Dimensions (SCD), are the dimensions in which the data changes slowly, rather 
+than changing regularly on a time basis.
+
+SCD and CDC data changes can be merged to a carbon dataset online using the data frame level `MERGE` API.
+
+#### MERGE API
+
+Below API merges the datasets online and applies the actions as per the conditions. 
+
+```
+  targetDS.merge(sourceDS, <condition>)
+          .whenMatched(<condition>)
+          .updateExpr(updateMap)
+          .insertExpr(insertMap_u)
+          .whenNotMatched(<condition>)
+          .insertExpr(insertMap)
+          .whenNotMatchedAndExistsOnlyOnTarget(<condition>)
+          .delete()
+          .insertHistoryTableExpr(insertMap_d, <table_name>)
+          .execute()
+```
+**NOTE:** SQL syntax for merge is not yet supported.
+
+##### Example code sample to implement ccd scenario

Review comment:
       Just give a link to `MergeTestCase.scala` and test case name
   No need have same thing here




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