PartiQL Select Statements for DynamoDB - Amazon DynamoDB

PartiQL Select Statements for DynamoDB

Use the SELECT statement to retrieve data from a table in Amazon DynamoDB.

Using the SELECT statement can result in a full table scan if an equality condition with a partition key is not provided in the WHERE clause. A scan operation examines every item for the requested values and can use up the provisioned throughput for a large table or index in a single operation.

If you want to avoid full table scan in PartiQL, you can:

For more information see Best Practices for Querying and Scanning Data, in the DynamoDB developer guide.

Syntax

SELECT expression [, ...] FROM table[.index] [ WHERE condition ] [ [ORDER BY key [DESC|ASC] , ...]

Parameters

expression

(Required) A projection formed from the * wildcard or a projection list of one or more attribute names or document paths from the result set. An expression can consist of calls to Use PartiQL Functions with Amazon DynamoDB or fields that are modified by PartiQL Arithmetic, Comparison, and Logical Operators for DynamoDB .

table

(Required) The table name to query.

index

(Optional) The name of the index to query.

condition

(Optional) The selection criteria for the query.

Important

To ensure that a SELECT statement does not result in a full table scan, the WHERE clause condition must specify a partition key. Use the equality or IN operator.

For example, if you have an Orders table with an OrderID partition key and other non-key attributes, including an Address, the following statements would not result in a full table scan:

SELECT * FROM Orders WHERE OrderID = 100 SELECT * FROM Orders WHERE OrderID = 100 and Address='some address' SELECT * FROM Orders WHERE OrderID = 100 or pk = 200 SELECT * FROM Orders WHERE OrderID IN [100, 300, 234]

The following SELECT statements, however, will result in a full table scan:

SELECT * FROM Orders WHERE OrderID > 1 SELECT * FROM Orders WHERE Address='some address' SELECT * FROM Orders WHERE OrderID = 100 OR Address='some address'
key

(Optional) A hash key or a sort key to use to order returned results. The default order is ascending (ASC) specify DESC if you want the results retuned in descending order.

Note

If you omit the WHERE clause, then all of the items in the table are retrieved.

Examples

The following query returns one item, if one exists, from the Orders table by specifying the partition key, OrderID, and using the equality operator.

SELECT OrderID, Total FROM Orders WHERE OrderID = 1

The following query returns all items in the Orders table that have a specific partition key, OrderID, values using the OR operator.

SELECT OrderID, Total FROM Orders WHERE OrderID = 1 OR OrderID = 2

The following query returns all items in the Orders table that have a specific partition key, OrderID, values using the IN operator. The returned results are in descending order, based on the OrderID key attribute value.

SELECT OrderID, Total FROM Orders WHERE OrderID IN [1, 2, 3] ORDER BY OrderID DESC

The following query shows a full table scan that returns all items from the Orders table that have a Total greater than 500, where Total is a non-key attribute.

SELECT OrderID, Total FROM Orders WHERE Total > 500

The following query shows a full table scan that returns all items from the Orders table within a specific Total order range, using the IN operator and a non-key attribute Total.

SELECT OrderID, Total FROM Orders WHERE Total IN [500, 600]

The following query shows a full table scan that returns all items from the Orders table within a specific Total order range, using the BETWEEN operator and a non-key attribute Total.

SELECT OrderID, Total FROM Orders WHERE Total BETWEEN 500 AND 600

The following query returns the first date a firestick device was used to watch by specifying the partition key CustomerID and sort key MovieID in the WHERE clause condition and using document paths in the SELECT clause.

SELECT Devices.FireStick.DateWatched[0] FROM WatchList WHERE CustomerID= 'C1' AND MovieID= 'M1'

The following query shows a full table scan that returns the list of items where a firestick device was first used after 12/12/19 using document paths in the WHERE clause condition.

SELECT Devices FROM WatchList WHERE Devices.FireStick.DateWatched[0] >= '12/12/19'