If I created the following NoSQL table using DynamoDB, how might I query for the item with the largest ID value whose Unused value is true without scanning the entire table?
(I have zero experience with cloud platforms and NoSQL.)
+--------+------------+-----------+
| ID | Unused | Token |
+--------+------------+-----------+
| 1 | True | ... |
+--------+------------+-----------+
| 2 | True | ... |
+--------+------------+-----------+
| 3 | True | ... |
+--------+------------+-----------+
| 4 | False | ... |
+--------+------------+-----------+
| 5 | False | ... |
+--------+------------+-----------+
You create a Global Secondary Index with Unused as the partition key and Id as the sort key.
| Unused | ID | Token |
|---|---|---|
| True | 1 | --- |
| True | 2 | --- |
| True | 3 | --- |
| False | 4 | --- |
| False | 5 | --- |
Using a Query you can do the following:
SELECT * FROM mytable.myindex WHERE Unused='True' LIMIT 1 DESC
This blog will help you to understand the pros and cons.