**Example 1: To update an item in a table** The following ``update-item`` example updates an item in the ``MusicCollection`` table. It adds a new attribute (``Year``) and modifies the ``AlbumTitle`` attribute. All of the attributes in the item, as they appear after the update, are returned in the response. :: aws dynamodb update-item \ --table-name MusicCollection \ --key file://key.json \ --update-expression "SET #Y = :y, #AT = :t" \ --expression-attribute-names file://expression-attribute-names.json \ --expression-attribute-values file://expression-attribute-values.json \ --return-values ALL_NEW \ --return-consumed-capacity TOTAL \ --return-item-collection-metrics SIZE Contents of ``key.json``:: { "Artist": {"S": "Acme Band"}, "SongTitle": {"S": "Happy Day"} } Contents of ``expression-attribute-names.json``:: { "#Y":"Year", "#AT":"AlbumTitle" } Contents of ``expression-attribute-values.json``:: { ":y":{"N": "2015"}, ":t":{"S": "Louder Than Ever"} } Output:: { "Attributes": { "AlbumTitle": { "S": "Louder Than Ever" }, "Awards": { "N": "10" }, "Artist": { "S": "Acme Band" }, "Year": { "N": "2015" }, "SongTitle": { "S": "Happy Day" } }, "ConsumedCapacity": { "TableName": "MusicCollection", "CapacityUnits": 3.0 }, "ItemCollectionMetrics": { "ItemCollectionKey": { "Artist": { "S": "Acme Band" } }, "SizeEstimateRangeGB": [ 0.0, 1.0 ] } } For more information, see `Writing an Item <https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/WorkingWithItems.html#WorkingWithItems.WritingData>`__ in the *Amazon DynamoDB Developer Guide*. **Example 2: To update an item conditionally** The following example updates an item in the ``MusicCollection`` table, but only if the existing item does not already have a ``Year`` attribute. :: aws dynamodb update-item \ --table-name MusicCollection \ --key file://key.json \ --update-expression "SET #Y = :y, #AT = :t" \ --expression-attribute-names file://expression-attribute-names.json \ --expression-attribute-values file://expression-attribute-values.json \ --condition-expression "attribute_not_exists(#Y)" Contents of ``key.json``:: { "Artist": {"S": "Acme Band"}, "SongTitle": {"S": "Happy Day"} } Contents of ``expression-attribute-names.json``:: { "#Y":"Year", "#AT":"AlbumTitle" } Contents of ``expression-attribute-values.json``:: { ":y":{"N": "2015"}, ":t":{"S": "Louder Than Ever"} } If the item already has a ``Year`` attribute, DynamoDB returns the following output. :: An error occurred (ConditionalCheckFailedException) when calling the UpdateItem operation: The conditional request failed For more information, see `Writing an Item <https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/WorkingWithItems.html#WorkingWithItems.WritingData>`__ in the *Amazon DynamoDB Developer Guide*.