builtins: add avg for interval

This PR adds the ability to average intervals. Comes with a few extra
tests for aggregation functions over intervals.

Release note (sql change): Adds the ability to run `avg` over intervals.

docs/generated/sql/aggregates.md

@@ -37,6 +37,8 @@
 </span></td></tr>
 <tr><td><a name="avg"></a><code>avg(arg1: <a href="int.html">int</a>) &rarr; <a href="decimal.html">decimal</a></code></td><td><span class="funcdesc"><p>Calculates the average of the selected values.</p>
 </span></td></tr>
+<tr><td><a name="avg"></a><code>avg(arg1: <a href="interval.html">interval</a>) &rarr; <a href="interval.html">interval</a></code></td><td><span class="funcdesc"><p>Calculates the average of the selected values.</p>
+</span></td></tr>
 <tr><td><a name="bit_and"></a><code>bit_and(arg1: <a href="int.html">int</a>) &rarr; <a href="int.html">int</a></code></td><td><span class="funcdesc"><p>Calculates the bitwise AND of all non-null input values, or null if none.</p>
 </span></td></tr>
 <tr><td><a name="bit_or"></a><code>bit_or(arg1: <a href="int.html">int</a>) &rarr; <a href="int.html">int</a></code></td><td><span class="funcdesc"><p>Calculates the bitwise OR of all non-null input values, or null if none.</p>

pkg/sql/logictest/testdata/logic_test/aggregate

@@ -5,7 +5,8 @@ CREATE TABLE kv (
   k INT PRIMARY KEY,
   v INT,
   w INT,
-  s STRING
+  s STRING,
+  i INTERVAL
 )
 
 # Aggregate functions return NULL if there are no rows.
@@ -36,6 +37,11 @@ SELECT jsonb_agg(1) FROM kv
 ----
 NULL
 
+query TTTT
+SELECT min(i), avg(i), max(i), sum(i) FROM kv
+----
+NULL NULL NULL NULL
+
 query IIIIRRRRBBT
 SELECT min(v), max(v), count(v), sum_int(1), avg(v), sum(v), stddev(v), variance(v), bool_and(v = 1), bool_and(v = 1), xor_agg(s::bytes) FROM kv
 ----
@@ -147,12 +153,12 @@ SELECT (SELECT COALESCE(max(1), 0) FROM generate_series(1,0))
 
 statement OK
 INSERT INTO kv VALUES
-(1, 2, 3, 'a'),
-(3, 4, 5, 'a'),
-(5, NULL, 5, NULL),
-(6, 2, 3, 'b'),
-(7, 2, 2, 'b'),
-(8, 4, 2, 'A')
+(1, 2, 3, 'a', '1min'::interval),
+(3, 4, 5, 'a', '2sec'::interval),
+(5, NULL, 5, NULL, NULL),
+(6, 2, 3, 'b', '1ms'::interval),
+(7, 2, 2, 'b', '4 days'::interval),
+(8, 4, 2, 'A', '3 years'::interval)
 
 # Aggregate functions triggers aggregation and computation for every row even when applied to a constant.
 # NB: The XOR result is 00 because \x01 is XOR'd an even number of times.
@@ -595,6 +601,11 @@ SELECT avg(k), avg(v), sum(k), sum(v) FROM kv
 ----
 5 2.8 30 14
 
+query TTTT
+SELECT min(i), avg(i), max(i), sum(i) FROM kv
+----
+00:00:00.001  7 mons 6 days 19:12:12.4002  3 years  3 years 4 days 00:01:02.001
+
 query RRRR
 SELECT avg(k::decimal), avg(v::decimal), sum(k::decimal), sum(v::decimal) FROM kv
 ----

pkg/sql/sem/builtins/aggregate_builtins.go

@@ -125,6 +125,8 @@ var aggregates = map[string]builtinDefinition{
 			"Calculates the average of the selected values."),
 		makeAggOverload([]*types.T{types.Decimal}, types.Decimal, newDecimalAvgAggregate,
 			"Calculates the average of the selected values."),
+		makeAggOverload([]*types.T{types.Interval}, types.Interval, newIntervalAvgAggregate,
+			"Calculates the average of the selected values."),
 	),
 
 	"bit_and": makeBuiltin(aggProps(),
@@ -571,6 +573,11 @@ func newDecimalAvgAggregate(
 ) tree.AggregateFunc {
 	return &avgAggregate{agg: newDecimalSumAggregate(params, evalCtx, arguments)}
 }
+func newIntervalAvgAggregate(
+	params []*types.T, evalCtx *tree.EvalContext, arguments tree.Datums,
+) tree.AggregateFunc {
+	return &avgAggregate{agg: newIntervalSumAggregate(params, evalCtx, arguments)}
+}
 
 // Add accumulates the passed datum into the average.
 func (a *avgAggregate) Add(ctx context.Context, datum tree.Datum, other ...tree.Datum) error {
@@ -600,6 +607,8 @@ func (a *avgAggregate) Result() (tree.Datum, error) {
 		count := apd.New(int64(a.count), 0)
 		_, err := tree.DecimalCtx.Quo(&t.Decimal, &t.Decimal, count)
 		return t, err
+	case *tree.DInterval:
+		return &tree.DInterval{Duration: t.Duration.Div(int64(a.count))}, nil
 	default:
 		return nil, errors.AssertionFailedf("unexpected SUM result type: %s", t)
 	}

pkg/sql/sem/builtins/aggregate_builtins_test.go

@@ -78,6 +78,11 @@ func TestAvgDecimalResultDeepCopy(t *testing.T) {
 	testAggregateResultDeepCopy(t, newDecimalAvgAggregate, makeDecimalTestDatum(10))
 }
 
+func TestAvgIntervalResultDeepCopy(t *testing.T) {
+	defer leaktest.AfterTest(t)()
+	testAggregateResultDeepCopy(t, newIntervalAvgAggregate, makeIntervalTestDatum(10))
+}
+
 func TestBitAndIntResultDeepCopy(t *testing.T) {
 	defer leaktest.AfterTest(t)()
 	t.Run("all null", func(t *testing.T) {
@@ -405,6 +410,14 @@ func BenchmarkAvgAggregateDecimal(b *testing.B) {
 	}
 }
 
+func BenchmarkAvgAggregateInterval(b *testing.B) {
+	for _, count := range []int{1000} {
+		b.Run(fmt.Sprintf("count=%d", count), func(b *testing.B) {
+			runBenchmarkAggregate(b, newIntervalAvgAggregate, makeIntervalTestDatum(count))
+		})
+	}
+}
+
 func BenchmarkCountAggregate(b *testing.B) {
 	for _, count := range []int{1000} {
 		b.Run(fmt.Sprintf("count=%d", count), func(b *testing.B) {