keyConditionExpression

The condition that specifies the key values for items to be retrieved by the Query action.

The condition must perform an equality test on a single partition key value.

The condition can optionally perform one of several comparison tests on a single sort key value. This allows Query to retrieve one item with a given partition key value and sort key value, or several items that have the same partition key value but different sort key values.

The partition key equality test is required, and must be specified in the following format:

partitionKeyName=:partitionkeyval

If you also want to provide a condition for the sort key, it must be combined using AND with the condition for the sort key. Following is an example, using the = comparison operator for the sort key:

partitionKeyName``=``:partitionkeyval``AND``sortKeyName``=``:sortkeyval

Valid comparisons for the sort key condition are as follows:

• sortKeyName``=``:sortkeyval - true if the sort key value is equal to :sortkeyval.

• sortKeyName``<``:sortkeyval - true if the sort key value is less than :sortkeyval.

• sortKeyName``<=``:sortkeyval - true if the sort key value is less than or equal to :sortkeyval.

• sortKeyName``>``:sortkeyval - true if the sort key value is greater than :sortkeyval.

• sortKeyName``>= ``:sortkeyval - true if the sort key value is greater than or equal to :sortkeyval.

• sortKeyName``BETWEEN``:sortkeyval1``AND``:sortkeyval2 - true if the sort key value is greater than or equal to :sortkeyval1, and less than or equal to :sortkeyval2.

• begins_with (``sortKeyName, :sortkeyval``) - true if the sort key value begins with a particular operand. (You cannot use this function with a sort key that is of type Number.) Note that the function name begins_with is case-sensitive.

Use the ExpressionAttributeValues parameter to replace tokens such as :partitionval and :sortval with actual values at runtime.

You can optionally use the ExpressionAttributeNames parameter to replace the names of the partition key and sort key with placeholder tokens. This option might be necessary if an attribute name conflicts with a DynamoDB reserved word. For example, the following KeyConditionExpression parameter causes an error because Size is a reserved word:

• Size = :myval

To work around this, define a placeholder (such a #S) to represent the attribute name Size. KeyConditionExpression then is as follows:

• #S = :myval

For a list of reserved words, see Reserved Words in the Amazon DynamoDB Developer Guide.

For more information on ExpressionAttributeNames and ExpressionAttributeValues, see Using Placeholders for Attribute Names and Values in the Amazon DynamoDB Developer Guide.