adding some tests and changelog message

Author: Brian Rowe

Changelog.md

@@ -7,11 +7,14 @@ This changelog should be updated as part of a PR if the work is worth noting (mo
 ## Next Release (Date TBD)
 
 #### New experimental features
-- [#615](https://github.com/timescale/timescaledb-toolkit/pull/614): Heatbeat aggregate
+- [#615](https://github.com/timescale/timescaledb-toolkit/pull/615): Heatbeat aggregate
   Users can use the new `heartbeat_agg(timestamp, start_time, agg_interval, heartbeat_interval)` to track the liveness of a system in the range (`start_time`, `start_time` + `agg_interval`). Each timestamp seen in that range is assumed to indicate system liveness for the following `heartbeat_interval`.
   Once constructed, users can query heartbeat aggregates for `uptime` and `downtime`, as well as query for `live_ranges` or `dead_ranges`. Users can also check for `live_at(timestamp)`.
   Heartbeat aggregates can also interpolated to better see behavior around the boundaries of the individual aggregates.
 
+- [#635](https://github.com/timescale/timescaledb-toolkit/pull/635): AsOf joins for timevectors
+  This allows users to join two timevectors with the following semantics `timevectorA -> asof(timevectorB)`. This will return records with the LOCF value from timevectorA at the timestamps from timevectorB. Specifically the returned records contain, for each value in timevectorB, {the LOCF value from timevectorA, the value from timevectorB, the timestamp from timevectorB}.
+
 #### Bug fixes
 - [#624](https://github.com/timescale/timescaledb-toolkit/pull/624): Remove partial aggregation for Candlestick aggregates.
   We've determined that the cause for the bad results lives somewhere in the functions that are used to support partial aggregation.

extension/src/time_vector.rs

@@ -775,4 +775,44 @@ mod tests {
             assert!(result.next().is_none());
         })
     }
+
+    #[pg_test(error = "both timevectors must be populated for an asof join")]
+    fn test_asof_none() {
+        Spi::execute(|client| {
+            client.select("SET timezone TO 'UTC'", None, None);
+
+            client.select(
+                "WITH s as (
+                    SELECT timevector(now(), 0) -> toolkit_experimental.filter($$ $value != 0 $$) AS empty),
+                    t as (
+                        SELECT timevector(time, value) AS valid FROM
+                        (VALUES 
+                            ('2022-10-1 0:30 UTC'::TIMESTAMPTZ, 15.0),
+                            ('2022-10-1 2:00 UTC'::TIMESTAMPTZ, 45.0),
+                            ('2022-10-1 3:30 UTC'::TIMESTAMPTZ, 60.0)
+                        ) as v(time, value))
+                    SELECT (valid -> toolkit_experimental.asof(empty))
+                    FROM s, t;", None, None);
+        })
+    }
+
+    #[pg_test(error = "both timevectors must be populated for an asof join")]
+    fn test_none_asof() {
+        Spi::execute(|client| {
+            client.select("SET timezone TO 'UTC'", None, None);
+
+            client.select(
+                "WITH s as (
+                    SELECT timevector(now(), 0) -> toolkit_experimental.filter($$ $value != 0 $$) AS empty),
+                    t as (
+                        SELECT timevector(time, value) AS valid FROM
+                        (VALUES 
+                            ('2022-10-1 0:30 UTC'::TIMESTAMPTZ, 15.0),
+                            ('2022-10-1 2:00 UTC'::TIMESTAMPTZ, 45.0),
+                            ('2022-10-1 3:30 UTC'::TIMESTAMPTZ, 60.0)
+                        ) as v(time, value))
+                    SELECT (empty -> toolkit_experimental.asof(valid))
+                    FROM s, t;", None, None);
+        })
+    }
 }