DynamoDBでソートキーを持つGSIに対してソートキーを指定しないクエリができるのか確認してみた

$ aws dynamodb describe-table --table-name object
{
    "Table": {
        "AttributeDefinitions": [
            {
                "AttributeName": "createdAt",
                "AttributeType": "N"
            },
            {
                "AttributeName": "objectId",
                "AttributeType": "S"
            },
            {
                "AttributeName": "objectType",
                "AttributeType": "S"
            }
        ],
        "TableName": "object",
        "KeySchema": [
            {
                "AttributeName": "objectId",
                "KeyType": "HASH"
            }
        ],
        "TableStatus": "ACTIVE",
        "CreationDateTime": 1594746956.736,
        "ProvisionedThroughput": {
            "NumberOfDecreasesToday": 0,
            "ReadCapacityUnits": 5,
            "WriteCapacityUnits": 5
        },
        "TableSizeBytes": 0,
        "ItemCount": 0,
        "TableArn": "arn:aws:dynamodb:ap-northeast-1:123456789012:table/object",
        "TableId": "262fab9b-b5d7-490a-b9a1-74f92a2272d3",
        "GlobalSecondaryIndexes": [
            {
                "IndexName": "objectType-createdAt-index",
                "KeySchema": [
                    {
                        "AttributeName": "objectType",
                        "KeyType": "HASH"
                    },
                    {
                        "AttributeName": "createdAt",
                        "KeyType": "RANGE"
                    }
                ],
                "Projection": {
                    "ProjectionType": "ALL"
                },
                "IndexStatus": "ACTIVE",
                "ProvisionedThroughput": {
                    "NumberOfDecreasesToday": 0,
                    "ReadCapacityUnits": 5,
                    "WriteCapacityUnits": 5
                },
                "IndexSizeBytes": 0,
                "ItemCount": 0,
                "IndexArn": "arn:aws:dynamodb:ap-northeast-1:123456789012:table/object/index/objectType-createdAt-index"
            }
        ]
    }
}

$ aws dynamodb query --table-name object \
    --index-name objectType-createdAt-index \
    --key-condition-expression "objectType = :type" \
    --expression-attribute-values  '{":type":{"S":"group"}}'

{
    "Items": [
        {
            "objectType": {
                "S": "group"
            },
            "createdAt": {
                "N": "11111111"
            },
            "objectId": {
                "S": "g0001"
            }
        }
    ],
    "Count": 1,
    "ScannedCount": 1,
    "ConsumedCapacity": null
}