Request Syntax Request Parameters Response Syntax Response Elements Errors Examples See Also

Scan

The Scan operation returns one or more items and item attributes by accessing every item in a table or a secondary index. To have DynamoDB return fewer items, you can provide a FilterExpression operation.

If the total size of scanned items exceeds the maximum dataset size limit of 1 MB, the scan completes and results are returned to the user. The LastEvaluatedKey value is also returned and the requestor can use the LastEvaluatedKey to continue the scan in a subsequent operation. Each scan response also includes number of items that were scanned (ScannedCount) as part of the request. If using a FilterExpression, a scan result can result in no items meeting the criteria and the Count will result in zero. If you did not use a FilterExpression in the scan request, then Count is the same as ScannedCount.

Note

Count and ScannedCount only return the count of items specific to a single scan request and, unless the table is less than 1MB, do not represent the total number of items in the table.

A single Scan operation first reads up to the maximum number of items set (if using the Limit parameter) or a maximum of 1 MB of data and then applies any filtering to the results if a FilterExpression is provided. If LastEvaluatedKey is present in the response, pagination is required to complete the full table scan. For more information, see Paginating the Results in the Amazon DynamoDB Developer Guide.

Scan operations proceed sequentially; however, for faster performance on a large table or secondary index, applications can request a parallel Scan operation by providing the Segment and TotalSegments parameters. For more information, see Parallel Scan in the Amazon DynamoDB Developer Guide.

By default, a Scan uses eventually consistent reads when accessing the items in a table. Therefore, the results from an eventually consistent Scan may not include the latest item changes at the time the scan iterates through each item in the table. If you require a strongly consistent read of each item as the scan iterates through the items in the table, you can set the ConsistentRead parameter to true. Strong consistency only relates to the consistency of the read at the item level.

Note

DynamoDB does not provide snapshot isolation for a scan operation when the ConsistentRead parameter is set to true. Thus, a DynamoDB scan operation does not guarantee that all reads in a scan see a consistent snapshot of the table when the scan operation was requested.

Request Syntax


{
   "AttributesToGet": [ "string" ],
   "ConditionalOperator": "string",
   "ConsistentRead": boolean,
   "ExclusiveStartKey": { 
      "string" : { 
         "B": blob,
         "BOOL": boolean,
         "BS": [ blob ],
         "L": [ 
            "AttributeValue"
         ],
         "M": { 
            "string" : "AttributeValue"
         },
         "N": "string",
         "NS": [ "string" ],
         "NULL": boolean,
         "S": "string",
         "SS": [ "string" ]
      }
   },
   "ExpressionAttributeNames": { 
      "string" : "string" 
   },
   "ExpressionAttributeValues": { 
      "string" : { 
         "B": blob,
         "BOOL": boolean,
         "BS": [ blob ],
         "L": [ 
            "AttributeValue"
         ],
         "M": { 
            "string" : "AttributeValue"
         },
         "N": "string",
         "NS": [ "string" ],
         "NULL": boolean,
         "S": "string",
         "SS": [ "string" ]
      }
   },
   "FilterExpression": "string",
   "IndexName": "string",
   "Limit": number,
   "ProjectionExpression": "string",
   "ReturnConsumedCapacity": "string",
   "ScanFilter": { 
      "string" : { 
         "AttributeValueList": [ 
            { 
               "B": blob,
               "BOOL": boolean,
               "BS": [ blob ],
               "L": [ 
                  "AttributeValue"
               ],
               "M": { 
                  "string" : "AttributeValue"
               },
               "N": "string",
               "NS": [ "string" ],
               "NULL": boolean,
               "S": "string",
               "SS": [ "string" ]
            }
         ],
         "ComparisonOperator": "string"
      }
   },
   "Segment": number,
   "Select": "string",
   "TableName": "string",
   "TotalSegments": number
}

Request Parameters

The request accepts the following data in JSON format.

Note

In the following list, the required parameters are described first.

TableName

The name of the table containing the requested items or if you provide IndexName, the name of the table to which that index belongs.

You can also provide the Amazon Resource Name (ARN) of the table in this parameter.

Type: String

Length Constraints: Minimum length of 1. Maximum length of 1024.

Required: Yes

AttributesToGet

This is a legacy parameter. Use ProjectionExpression instead. For more information, see AttributesToGet in the Amazon DynamoDB Developer Guide.

Type: Array of strings

Array Members: Minimum number of 1 item.

Length Constraints: Maximum length of 65535.

Required: No

ConditionalOperator

This is a legacy parameter. Use FilterExpression instead. For more information, see ConditionalOperator in the Amazon DynamoDB Developer Guide.

Type: String

Valid Values: AND | OR

Required: No

ConsistentRead

A Boolean value that determines the read consistency model during the scan:

If ConsistentRead is false, then the data returned from Scan might not contain the results from other recently completed write operations (PutItem, UpdateItem, or DeleteItem).
If ConsistentRead is true, then all of the write operations that completed before the Scan began are guaranteed to be contained in the Scan response.

The default setting for ConsistentRead is false.

The ConsistentRead parameter is not supported on global secondary indexes. If you scan a global secondary index with ConsistentRead set to true, you will receive a ValidationException.

Type: Boolean

Required: No

ExclusiveStartKey

The primary key of the first item that this operation will evaluate. Use the value that was returned for LastEvaluatedKey in the previous operation.

The data type for ExclusiveStartKey must be String, Number or Binary. No set data types are allowed.

In a parallel scan, a Scan request that includes ExclusiveStartKey must specify the same segment whose previous Scan returned the corresponding value of LastEvaluatedKey.

Type: String to AttributeValue object map

Key Length Constraints: Maximum length of 65535.

Required: No

ExpressionAttributeNames

One or more substitution tokens for attribute names in an expression. The following are some use cases for using ExpressionAttributeNames:

To access an attribute whose name conflicts with a DynamoDB reserved word.
To create a placeholder for repeating occurrences of an attribute name in an expression.