docs: explain `ChunkOrder` query test scenario
@@ -1170,6 +1170,21 @@ impl DbSetup for ChunkOrder {
.clear_lifecycle_action()
.unwrap();
+ // Now we have the the following chunks (same partition and table):
+ //
+ // | ID | order | tag: region | field: user | time |
+ // | -- | ----- | ----------- | ----------- | ---- |
+ // | 1 | 1 | "west" | 2 | 100 |
+ // | 2 | 0 | "west" | 1 | 100 |
+ //
+ // The result after deduplication should be:
+ //
+ // | tag: region | field: user | time |
+ // | ----------- | ----------- | ---- |
+ // | "west" | 2 | 100 |
+ //
+ // So the query engine must use `order` as a primary key to sort chunks, NOT `id`.
+
let scenario = DbScenario {
scenario_name: "chunks where chunk ID alone cannot be used for ordering".into(),
db,
