Scanning a Table - Amazon DynamoDB

Scanning a Table

In SQL, a SELECT statement without a WHERE clause will return every row in a table. In Amazon DynamoDB, the Scan operation does the same thing. In both cases, you can retrieve all of the items or just some of them.

Whether you are using a SQL or a NoSQL database, scans should be used sparingly because they can consume large amounts of system resources. Sometimes a scan is appropriate (such as scanning a small table) or unavoidable (such as performing a bulk export of data). However, as a general rule, you should design your applications to avoid performing scans.

Topics

SQL

In SQL, you can scan a table and retrieve all of its data by using a SELECT statement without specifying a WHERE clause. You can request one or more columns in the result. Or you can request all of them if you use the wildcard character (*).

The following are examples of using a SELECT statement.

/* Return all of the data in the table */ SELECT * FROM Music;
/* Return all of the values for Artist and Title */ SELECT Artist, Title FROM Music;

DynamoDB

PartiQL

DynamoDB provides the ExecuteStatement to return all the contents for a table using the select statement.

select AlbumTitle, Year, Price FROM Music

Note that this statement will return all items for in the Music table.

For code examples using Select and ExecuteStatement, see PartiQL Select Statements for DynamoDB.

Classic APIs

DynamoDB provides a Scan action that works in a similar way. The following are some examples.

// Return all of the data in the table { TableName: "Music" }
// Return all of the values for Artist and Title { TableName: "Music", ProjectionExpression: "Artist, Title" }

The Scan action also provides a FilterExpression parameter, which you can use to discard items that you do not want to appear in the results. A FilterExpression is applied after the scan is performed, but before the results are returned to you. (This is not recommended with large tables. You are still charged for the entire Scan, even if only a few matching items are returned.)

Note

For code examples that use Scan, see Getting Started with DynamoDB and AWS SDKs.