sql: fix float to integer casting

Previously, casting a float value to an integer simply truncates the float.
This commit fixes that by rounding the float value to the nearest integer,
rounding ties to even, as in postgres.

Epic: None
Fixes: #112515

Release note (bug fix): A bug has been fixed where casts of floats to integers
truncated the value. These casts now round a float to the nearest integer,
rounding ties to even integers.

pkg/ccl/logictestccl/testdata/logic_test/udf_plpgsql

@@ -2405,7 +2405,6 @@ subtest plpgsql_types
 # If an assignment cast is available, the cast is performed automatically.
 #
 # float -> int
-# TODO(112515): the float value is incorrectly truncated instead of rounded.
 statement ok
 DROP FUNCTION F();
 CREATE OR REPLACE FUNCTION f() RETURNS INT AS $$
@@ -2417,7 +2416,7 @@ $$ LANGUAGE PLpgSQL;
 query I
 SELECT f();
 ----
-105
+106
 
 # decimal -> int
 statement ok

pkg/sql/colexec/execgen/cmd/execgen/cast_gen_util.go

@@ -271,7 +271,7 @@ func floatToInt(intWidth, floatWidth int32) castFunc {
 			if math.IsNaN(float64(%[2]s)) || %[2]s <= float%[4]d(math.MinInt%[3]d) || %[2]s >= float%[4]d(math.MaxInt%[3]d) {
 				colexecerror.ExpectedError(tree.ErrIntOutOfRange)
 			}
-			%[1]s = int%[3]d(%[2]s)
+			%[1]s = int%[3]d(math.RoundToEven(%[2]s))
 		`
 		if intWidth == anyWidth {
 			intWidth = 64

pkg/sql/logictest/testdata/logic_test/aggregate

@@ -989,12 +989,12 @@ UPDATE mnop SET o = n::decimal, p = (n * 10)::bigint
 query RRR
 SELECT round(variance(n), 2), round(variance(n), 2), round(variance(p)) FROM mnop
 ----
-0.08 0.08 8
+0.08 0.08 9
 
 query RRR
 SELECT round(var_pop(n), 2), round(var_pop(n), 2), round(var_pop(p)) FROM mnop
 ----
-0.08 0.08 8
+0.08 0.08 9
 
 query RRR
 SELECT round(stddev_samp(n), 2), round(stddev(n), 2), round(stddev_samp(p)) FROM mnop

pkg/sql/logictest/testdata/logic_test/target_names

@@ -73,4 +73,4 @@ SELECT (SELECT 123 AS a),
        (SELECT cos(0)::INT)
 ----
 a   column1 cos
-123 0       1
+123 1       1

pkg/sql/sem/eval/cast.go

@@ -220,7 +220,7 @@ func performCastWithoutPrecisionTruncation(
 			if math.IsNaN(f) || f <= float64(math.MinInt64) || f >= float64(math.MaxInt64) {
 				return nil, tree.ErrIntOutOfRange
 			}
-			res = tree.NewDInt(tree.DInt(f))
+			res = tree.NewDInt(tree.DInt(math.RoundToEven(f)))
 		case *tree.DDecimal:
 			i, err := roundDecimalToInt(&v.Decimal)
 			if err != nil {

pkg/sql/sem/eval/testdata/eval/cast

@@ -1460,3 +1460,25 @@ eval
 text(1.11::float8)
 ----
 '1.11'
+
+# Issue #112515: float casting returns the nearest integer,
+# rounding ties to even (Banker's rounding).
+eval
+int8(0.5::float8)
+----
+0
+
+eval
+int8(1.5::float8)
+----
+2
+
+eval
+int8(-0.5::float8)
+----
+0
+
+eval
+int8(-1.5::float8)
+----
+-2