sql: Add support for numeric JSON scalar casts

* Fixes cockroachdb#41333
* Add support for queries such as
  - `SELECT '1'::jsonb::int`
  - `SELECT '1'::jsonb::float`
  - `SELECT '3.14'::jsonb::decimal`

Release note: None

pkg/sql/sem/tree/eval.go

@@ -3213,6 +3213,18 @@ func PerformCast(ctx *EvalContext, d Datum, t *types.T) (Datum, error) {
 			res = NewDInt(DInt(iv))
 		case *DOid:
 			res = &v.DInt
+		case *DJSON:
+			if v.Type() == json.NumberJSONType {
+				// err is ignored as a more appropriate error
+				// will be generated later
+				dec, err := json.ToDecimal(v.JSON)
+				if err == nil {
+					asInt, err := dec.Int64()
+					if err == nil {
+						res = NewDInt(DInt(asInt))
+					}
+				}
+			}
 		}
 		if res != nil {
 			return res, nil
@@ -3253,6 +3265,18 @@ func PerformCast(ctx *EvalContext, d Datum, t *types.T) (Datum, error) {
 			return NewDFloat(DFloat(float64(v.UnixEpochDays()))), nil
 		case *DInterval:
 			return NewDFloat(DFloat(v.AsFloat64())), nil
+		case *DJSON:
+			if v.Type() == json.NumberJSONType {
+				// err is ignored as a more appropriate error
+				// will be generated later
+				dec, err := json.ToDecimal(v.JSON)
+				if err == nil {
+					asFloat, err := dec.Int64()
+					if err == nil {
+						return NewDFloat(DFloat(asFloat)), nil
+					}
+				}
+			}
 		}
 
 	case types.DecimalFamily:
@@ -3301,6 +3325,15 @@ func PerformCast(ctx *EvalContext, d Datum, t *types.T) (Datum, error) {
 		case *DInterval:
 			v.AsBigInt(&dd.Coeff)
 			dd.Exponent = -9
+		case *DJSON:
+			if v.Type() == json.NumberJSONType {
+				var dec apd.Decimal
+				// err is ignored as a more appropriate error
+				// will be generated later
+				dec, err = json.ToDecimal(v.JSON)
+				unset = err != nil
+				dd = DDecimal{dec}
+			}
 		default:
 			unset = true
 		}

pkg/sql/sem/tree/expr.go

@@ -1520,11 +1520,11 @@ var (
 	bitArrayCastTypes = annotateCast(types.VarBit, []*types.T{types.Unknown, types.VarBit, types.Int, types.String, types.AnyCollatedString})
 	boolCastTypes     = annotateCast(types.Bool, []*types.T{types.Unknown, types.Bool, types.Int, types.Float, types.Decimal, types.String, types.AnyCollatedString})
 	intCastTypes      = annotateCast(types.Int, []*types.T{types.Unknown, types.Bool, types.Int, types.Float, types.Decimal, types.String, types.AnyCollatedString,
-		types.Timestamp, types.TimestampTZ, types.Date, types.Interval, types.Oid, types.VarBit})
+		types.Timestamp, types.TimestampTZ, types.Date, types.Interval, types.Oid, types.VarBit, types.Jsonb})
 	floatCastTypes = annotateCast(types.Float, []*types.T{types.Unknown, types.Bool, types.Int, types.Float, types.Decimal, types.String, types.AnyCollatedString,
-		types.Timestamp, types.TimestampTZ, types.Date, types.Interval})
+		types.Timestamp, types.TimestampTZ, types.Date, types.Interval, types.Jsonb})
 	decimalCastTypes = annotateCast(types.Decimal, []*types.T{types.Unknown, types.Bool, types.Int, types.Float, types.Decimal, types.String, types.AnyCollatedString,
-		types.Timestamp, types.TimestampTZ, types.Date, types.Interval})
+		types.Timestamp, types.TimestampTZ, types.Date, types.Interval, types.Jsonb})
 	stringCastTypes = annotateCast(types.String, []*types.T{types.Unknown, types.Bool, types.Int, types.Float, types.Decimal, types.String, types.AnyCollatedString,
 		types.VarBit,
 		types.AnyArray, types.AnyTuple,

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

@@ -977,3 +977,58 @@ eval
 ARRAY['hello','world']::char(2)[]
 ----
 ARRAY['he','wo']
+
+eval
+'1'::jsonb::int
+----
+1
+
+eval
+'1'::jsonb::float
+----
+1.0
+
+eval
+'1'::jsonb::decimal
+----
+1
+
+eval
+'1'::jsonb::string
+----
+'1'
+
+eval
+'2.0'::jsonb::int
+----
+2
+
+eval
+'2.0'::jsonb::float
+----
+2.0
+
+eval
+'2.0'::jsonb::decimal
+----
+2.0
+
+eval
+'2.0'::jsonb::string
+----
+'2.0'
+
+eval
+'3.14'::jsonb::float
+----
+3.14
+
+eval
+'3.14'::jsonb::decimal
+----
+3.14
+
+eval
+'3.14'::jsonb::string
+----
+'3.14'

pkg/util/json/json.go

@@ -972,6 +972,19 @@ func FromFloat64(v float64) (JSON, error) {
 	return jsonNumber(dec), nil
 }
 
+// ToDecimal returns a apd.Decimal given a JSON value
+func ToDecimal(j JSON) (apd.Decimal, error) {
+	j, err := decodeIfNeeded(j)
+	if err != nil {
+		return apd.Decimal{}, err
+	}
+	num, ok := j.(jsonNumber)
+	if !ok {
+		return apd.Decimal{}, errors.AssertionFailedf("cannot convert JSON of type %T to decimal", j)
+	}
+	return apd.Decimal(num), nil
+}
+
 // MakeJSON returns a JSON value given a Go-style representation of JSON.
 // * JSON null is Go `nil`,
 // * JSON true is Go `true`,

pkg/util/json/json_test.go

@@ -2016,3 +2016,65 @@ func TestJSONRemovePath(t *testing.T) {
 		}
 	}
 }
+
+func TestToDecimal(t *testing.T) {
+	numericCases := []string{
+		"1",
+		"1.0",
+		"3.14",
+		"-3.14",
+		"1.000",
+		"-0.0",
+		"-0.09",
+		"0.08",
+	}
+
+	nonNumericCases := []struct {
+		input  string
+		errMsg string
+	}{
+		{"\"1\"", "cannot convert JSON of type json.jsonString to decimal"},
+		{"{}", "cannot convert JSON of type json.jsonObject to decimal"},
+		{"[]", "cannot convert JSON of type json.jsonArray to decimal"},
+		{"true", "cannot convert JSON of type json.jsonTrue to decimal"},
+		{"false", "cannot convert JSON of type json.jsonFalse to decimal"},
+		{"null", "cannot convert JSON of type json.jsonNull to decimal"},
+	}
+
+	for _, tc := range numericCases {
+		t.Run(fmt.Sprintf("numeric - %s", tc), func(t *testing.T) {
+			dec1, _, err := apd.NewFromString(tc)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			json, err := ParseJSON(tc)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			dec2, err := ToDecimal(json)
+			if err != nil {
+				t.Fatal(err)
+			}
+
+			if dec1.Cmp(&dec2) != 0 {
+				t.Fatalf("expected %s == %s", dec1.String(), dec2.String())
+			}
+		})
+	}
+
+	for _, tc := range nonNumericCases {
+		t.Run(fmt.Sprintf("nonNumeric - %s", tc), func(t *testing.T) {
+			json, err := ParseJSON(tc.input)
+			if err != nil {
+				t.Fatalf("expected no error")
+			}
+
+			_, err = ToDecimal(json)
+			if err.Error() != tc.errMsg {
+				t.Fatalf("expected %s, got %s", tc.errMsg, err.Error())
+			}
+		})
+	}
+}