Azure Cosmos DB SQL API UPDATE statement - don't replace whole document

The Cosmos DB SQL language only supports the Select statement.

Partially updating a document isn't supported via the sql language or the SQL API.

People have made it clear that that's a feature they want so there is a highly upvoted request for it that can be found here: https://feedback.azure.com/forums/263030-azure-cosmos-db/suggestions/6693091-be-able-to-do-partial-updates-on-document

Microsoft has already started to work on that so the only thing you can do is wait.

To elaborate more on this, Updating partially a document in CosmosDb on the server isn’t possible, instead you can do whatever you need to do in the memory.In order to literally UPDATE the document, you will have to to retrieve the entire document from the CosmosDb, update the property/properties that you need to update and then call the ‘Replace’ method in the CosmosDb SDK to replace the document in question. Alternatively you can also use ‘Upsert’ which checks if the document already exists and performs an ‘Insert’ if true or ‘Replace’ if false.

NOTE : Make sure you have the latest version of the document before you commit an update!

As Nick mentioned Cosmosdb team is working on the partial update.