Querying a Table

Another common access pattern is reading multiple items from a table, based on your query criteria.

SQL

The SQL SELECT statement lets you query on key columns, non-key columns, or any combination. The WHERE clause determines which rows are returned, as shown in the following examples.

/* Return a single song, by primary key */

SELECT * FROM Music
WHERE Artist='No One You Know' AND SongTitle = 'Call Me Today';

/* Return all of the songs by an artist */

SELECT * FROM Music
WHERE Artist='No One You Know';

/* Return all of the songs by an artist, matching first part of title */

SELECT * FROM Music
WHERE Artist='No One You Know' AND SongTitle LIKE 'Call%';

/* Return all of the songs by an artist, with a particular word in the title...
...but only if the price is less than 1.00 */

SELECT * FROM Music
WHERE Artist='No One You Know' AND SongTitle LIKE '%Today%'
AND Price < 1.00;

Note that the primary key for this table consists of Artist and SongTitle.

DynamoDB

The Amazon DynamoDB Query action lets you retrieve data in a similar fashion. The Query action provides quick, efficient access to the physical locations where the data is stored. For more information, see Partitions and Data Distribution.

You can use Query with any table that has a composite primary key (partition key and sort key). You must specify an equality condition for the partition key, and you can optionally provide another condition for the sort key.

The KeyConditionExpression parameter specifies the key values that you want to query. You can use an optional FilterExpression to remove certain items from the results before they are returned to you.

In DynamoDB, you must use ExpressionAttributeValues as placeholders in expression parameters (such as KeyConditionExpression and FilterExpression). This is analogous to the use of bind variables in relational databases, where you substitute the actual values into the SELECT statement at runtime.

Note that the primary key for this table consists of Artist and SongTitle.

The following are some DynamoDB Query examples.

// Return a single song, by primary key

{
    TableName: "Music",
    KeyConditionExpression: "Artist = :a and SongTitle = :t",
    ExpressionAttributeValues: {
        ":a": "No One You Know",
        ":t": "Call Me Today"
    }
}

// Return all of the songs by an artist

{
    TableName: "Music",
    KeyConditionExpression: "Artist = :a",
    ExpressionAttributeValues: {
        ":a": "No One You Know"
    }
}

// Return all of the songs by an artist, matching first part of title

{
    TableName: "Music",
    KeyConditionExpression: "Artist = :a and begins_with(SongTitle, :t)",
    ExpressionAttributeValues: {
        ":a": "No One You Know",
        ":t": "Call"
    }
}

Note

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