Update how-to-sqldb-to-cosmosdb.md

Author: kromerm

articles/data-factory/how-to-sqldb-to-cosmosdb.md

@@ -55,6 +55,10 @@ The resulting CosmosDB container will embed the inner query into a single docume
 
 6. Define the source for "SourceOrderHeader". For dataset, create a new Azure SQL Database dataset that points to the ```SalesOrderHeader``` table.
 
+7. On the top source, add a Derived Column transformation after "SourceOrderDetails". Call the new transformation "TypeCast". We need to round the ```UnitPrice``` column and cast it to a double data type for CosmosDB. Set the formula to: ```toDouble(round(UnitPrice,2))```.
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+8. 
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 ## Next steps
 
 * Build the rest of your data flow logic by using mapping data flows [transformations](concepts-data-flow-overview.md).