Querying a DynamoDb table using a combination of `begins_with` and `between` conditions

Question

How can I query a DynamoDb table using a combination of the BETWEEN and BEGINS_WITH ?

A simplified example of my tables partition and sort key looks like this:

PK    |SK
my_pk |2022-05-13T08:30:00Z#tag0
my_pk |2022-05-13T08:45:00Z#tag0
my_pk |2022-05-13T08:45:00Z#tag1
my_pk |2022-05-13T08:45:00Z#tag2
my_pk |2022-05-13T09:00:00Z#tag0
my_pk |2022-05-13T09:00:00Z#tag1

If my SK didn't include the ...#tag postfix I could use a KeyConditionExpression like this:

"KeyConditionExpression": "#pk = :pk AND #sk BETWEEN :start AND :end"

where start and end are eg 2022-05-13T08:45:00Z and 2022-05-13T09:00:00Z , respectively, but I am unsure how to do it when the postfix is there.

Note: I never need to query with the tag , it's just there to ensure that the composite primary key is unique.

Note2: I am using python and boto3 to execute the query.

Answer 1

You can use between where :end = 2022-05-13T09:00:00Z$ . Dollar sign is the next value after hash in ASCII, so this will capture all values starting with 2022-05-13T09:00:00Z# .

Answer 2

Partition and sort keys in a LSI or GSI do not need to be unique. So you can create an LSI, and use date column there as sort key.

This post exactly talks about this - Local Secondary Indexes .

Here is an screenshot from that page.

To ensure uniqueness in composite primary key, you can store some random string in sort key column.