sql: Add support for numeric JSON scalar casts

Previously, casting from a JSON numeric value to numeric values was
unspported.
This commit adds support for this feature allowing queries such as:
`SELECT '1'::jsonb::int`
`SELECT '1'::jsonb::float`
`SELECT '3.14'::jsonb::decimal`
to work as expected.

Fixes #41333

Release note (sql change): Casting JSON numeric scalars to numeric
                           types now works as expected.

pkg/sql/sem/tree/casts.go

@@ -98,6 +98,7 @@ var validCasts = []castInfo{
 	{from: types.IntervalFamily, to: types.IntFamily, volatility: VolatilityImmutable},
 	{from: types.OidFamily, to: types.IntFamily, volatility: VolatilityImmutable},
 	{from: types.BitFamily, to: types.IntFamily, volatility: VolatilityImmutable},
+	{from: types.JsonFamily, to: types.IntFamily, volatility: VolatilityImmutable},
 
 	// Casts to FloatFamily.
 	{from: types.UnknownFamily, to: types.FloatFamily, volatility: VolatilityImmutable},
@@ -111,6 +112,7 @@ var validCasts = []castInfo{
 	{from: types.TimestampTZFamily, to: types.FloatFamily, volatility: VolatilityImmutable},
 	{from: types.DateFamily, to: types.FloatFamily, volatility: VolatilityImmutable},
 	{from: types.IntervalFamily, to: types.FloatFamily, volatility: VolatilityImmutable},
+	{from: types.JsonFamily, to: types.FloatFamily, volatility: VolatilityImmutable},
 
 	// Casts to Box2D Family.
 	{from: types.UnknownFamily, to: types.Box2DFamily, volatility: VolatilityImmutable},
@@ -150,6 +152,7 @@ var validCasts = []castInfo{
 	{from: types.TimestampTZFamily, to: types.DecimalFamily, volatility: VolatilityImmutable},
 	{from: types.DateFamily, to: types.DecimalFamily, volatility: VolatilityImmutable},
 	{from: types.IntervalFamily, to: types.DecimalFamily, volatility: VolatilityImmutable},
+	{from: types.JsonFamily, to: types.DecimalFamily, volatility: VolatilityImmutable},
 
 	// Casts to StringFamily.
 	{from: types.UnknownFamily, to: types.StringFamily, volatility: VolatilityImmutable},
@@ -697,6 +700,13 @@ func performCastWithoutPrecisionTruncation(ctx *EvalContext, d Datum, t *types.T
 			res = NewDInt(DInt(iv))
 		case *DOid:
 			res = &v.DInt
+		case *DJSON:
+			if dec, ok := v.AsDecimal(); ok {
+				asInt, err := dec.Int64()
+				if err == nil {
+					res = NewDInt(DInt(asInt))
+				}
+			}
 		}
 		if res != nil {
 			return res, nil
@@ -747,6 +757,14 @@ func performCastWithoutPrecisionTruncation(ctx *EvalContext, d Datum, t *types.T
 			return NewDFloat(DFloat(float64(v.UnixEpochDays()))), nil
 		case *DInterval:
 			return NewDFloat(DFloat(v.AsFloat64())), nil
+		case *DJSON:
+			if dec, ok := v.AsDecimal(); ok {
+				fl, err := dec.Float64()
+				if err != nil {
+					return nil, ErrFloatOutOfRange
+				}
+				return NewDFloat(DFloat(fl)), nil
+			}
 		}
 
 	case types.DecimalFamily:
@@ -795,6 +813,12 @@ func performCastWithoutPrecisionTruncation(ctx *EvalContext, d Datum, t *types.T
 		case *DInterval:
 			v.AsBigInt(&dd.Coeff)
 			dd.Exponent = -9
+		case *DJSON:
+			if dec, ok := v.AsDecimal(); ok {
+				dd.Set(dec)
+			} else {
+				unset = false
+			}
 		default:
 			unset = true
 		}

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

@@ -1132,3 +1132,74 @@ eval
 'hello t'::string::char(100)
 ----
 'hello t'
+
+# Test that numeric jsonb values can be cast to a numeric data type
+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
+'true'::jsonb::float
+----
+invalid cast: jsonb -> float
+
+eval
+'null'::jsonb::float
+----
+invalid cast: jsonb -> float
+
+eval
+'{}'::jsonb::float
+----
+invalid cast: jsonb -> float
+
+eval
+'[]'::jsonb::float
+----
+invalid cast: jsonb -> float

pkg/util/json/encoded.go

@@ -17,6 +17,7 @@ import (
 	"strconv"
 	"unsafe"
 
+	"github.com/cockroachdb/apd/v2"
 	"github.com/cockroachdb/cockroach/pkg/sql/inverted"
 	"github.com/cockroachdb/cockroach/pkg/util/syncutil"
 	"github.com/cockroachdb/errors"
@@ -558,6 +559,18 @@ func (j *jsonEncoded) AsText() (*string, error) {
 	return decoded.AsText()
 }
 
+func (j *jsonEncoded) AsDecimal() (*apd.Decimal, bool) {
+	if dec := j.alreadyDecoded(); dec != nil {
+		return dec.AsDecimal()
+	}
+
+	decoded, err := j.decode()
+	if err != nil {
+		return nil, false
+	}
+	return decoded.AsDecimal()
+}
+
 func (j *jsonEncoded) Compare(other JSON) (int, error) {
 	if cmp := cmpJSONTypes(j.Type(), other.Type()); cmp != 0 {
 		return cmp, nil

pkg/util/json/json.go

@@ -136,6 +136,10 @@ type JSON interface {
 	// AsText returns the JSON document as a string, with quotes around strings removed, and null as nil.
 	AsText() (*string, error)
 
+	// AsDecimal returns the JSON document as a apd.Decimal if it is a numeric
+	// type, and a boolean inidicating if this JSON document is a numeric type.
+	AsDecimal() (*apd.Decimal, bool)
+
 	// Exists implements the `?` operator.
 	Exists(string) (bool, error)
 
@@ -412,6 +416,17 @@ func (j jsonString) MaybeDecode() JSON { return j }
 func (j jsonArray) MaybeDecode() JSON  { return j }
 func (j jsonObject) MaybeDecode() JSON { return j }
 
+func (j jsonNull) AsDecimal() (*apd.Decimal, bool)   { return nil, false }
+func (j jsonFalse) AsDecimal() (*apd.Decimal, bool)  { return nil, false }
+func (j jsonTrue) AsDecimal() (*apd.Decimal, bool)   { return nil, false }
+func (j jsonString) AsDecimal() (*apd.Decimal, bool) { return nil, false }
+func (j jsonArray) AsDecimal() (*apd.Decimal, bool)  { return nil, false }
+func (j jsonObject) AsDecimal() (*apd.Decimal, bool) { return nil, false }
+func (j jsonNumber) AsDecimal() (*apd.Decimal, bool) {
+	d := apd.Decimal(j)
+	return &d, true
+}
+
 func (j jsonNull) tryDecode() (JSON, error)   { return j, nil }
 func (j jsonFalse) tryDecode() (JSON, error)  { return j, nil }
 func (j jsonTrue) tryDecode() (JSON, error)   { return j, nil }

pkg/util/json/json_test.go

@@ -2252,3 +2252,62 @@ 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 := []string{
+		"\"1\"",
+		"{}",
+		"[]",
+		"true",
+		"false",
+		"null",
+	}
+
+	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, ok := json.AsDecimal()
+			if !ok {
+				t.Fatalf("could not cast %v to decmial", json)
+			}
+
+			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)
+			if err != nil {
+				t.Fatalf("expected no error")
+			}
+
+			dec, ok := json.AsDecimal()
+			if dec != nil || ok {
+				t.Fatalf("%v should not be a valid decimal", json)
+			}
+		})
+	}
+}