sql: replicating JSON empty array ordering found in Postgres

Currently, cockroachdb#97928 and cockroachdb#99275 are responsible for laying out
a lexicographical ordering for JSON columns to be forward
indexable in nature. This ordering is based on the rules
posted by Postgres and is defined here: cockroachdb#99849

However, Postgres currently sorts the empty JSON array
before any other JSON values. An issue has been opened:
https://www.postgresql.org/message-id/17873-826fdc8bbcace4f1%40postgresql.org

Thus, this PR intends on replicating this behaviour until
the issue has been identified and resolved by Postgres.

Epic: CRDB-24501

Release note (sql change): This PR shall now place the empty JSON array
to have the lowest (highest) precedence when the JSON column
is being sorted in ascending (descending) order.

pkg/sql/logictest/testdata/logic_test/json

@@ -1382,12 +1382,12 @@ INSERT INTO t VALUES
 query T
 SELECT x FROM t ORDER BY x;
 ----
+[]
 null
 "crdb"
 1
 false
 true
-[]
 [null]
 [1]
 [{"a": "b"}]
@@ -1430,12 +1430,12 @@ SELECT t1.x FROM t1 INNER LOOKUP JOIN t2 ON t1.x = t2.x
 query T
 SELECT x FROM t GROUP BY x ORDER BY x;
 ----
+[]
 null
 "crdb"
 1
 false
 true
-[]
 [null]
 [1]
 [{"a": "b"}]

pkg/sql/rowenc/keyside/json.go

@@ -79,7 +79,7 @@ func decodeJSONKey(buf []byte, dir encoding.Direction) (json.JSON, []byte, error
 		}
 		buf = buf[1:] // removing the terminator
 		jsonVal = json.FromDecimal(dec)
-	case encoding.JSONArray, encoding.JSONArrayDesc:
+	case encoding.JSONArray, encoding.JSONArrayDesc, encoding.JsonEmptyArray, encoding.JsonEmptyArrayDesc:
 		jsonVal, buf, err = decodeJSONArray(buf, dir)
 		if err != nil {
 			return nil, nil, errors.NewAssertionErrorWithWrappedErrf(err, "could not decode JSON Array")

pkg/util/encoding/encoding.go

@@ -106,13 +106,17 @@ const (
 
 	// Defining different key markers, for the ascending designation,
 	// for handling different JSON values.
-	jsonNullKeyMarker   = voidMarker + 1
-	jsonStringKeyMarker = jsonNullKeyMarker + 1
-	jsonNumberKeyMarker = jsonStringKeyMarker + 1
-	jsonFalseKeyMarker  = jsonNumberKeyMarker + 1
-	jsonTrueKeyMarker   = jsonFalseKeyMarker + 1
-	jsonArrayKeyMarker  = jsonTrueKeyMarker + 1
-	jsonObjectKeyMarker = jsonArrayKeyMarker + 1
+
+	// Postgres currently has a special case (maybe a bug) where
+	// the empty JSON Array sorts before all other JSON values.
+	jsonEmptyArrayKeyMarker = voidMarker + 1
+	jsonNullKeyMarker       = jsonEmptyArrayKeyMarker + 1
+	jsonStringKeyMarker     = jsonNullKeyMarker + 1
+	jsonNumberKeyMarker     = jsonStringKeyMarker + 1
+	jsonFalseKeyMarker      = jsonNumberKeyMarker + 1
+	jsonTrueKeyMarker       = jsonFalseKeyMarker + 1
+	jsonArrayKeyMarker      = jsonTrueKeyMarker + 1
+	jsonObjectKeyMarker     = jsonArrayKeyMarker + 1
 
 	arrayKeyTerminator           byte = 0x00
 	arrayKeyDescendingTerminator byte = 0xFF
@@ -126,13 +130,14 @@ const (
 
 	// Defining different key markers, for the descending designation,
 	// for handling different JSON values.
-	jsonNullKeyDescendingMarker   = jsonObjectKeyMarker + 7
-	jsonStringKeyDescendingMarker = jsonNullKeyDescendingMarker - 1
-	jsonNumberKeyDescendingMarker = jsonStringKeyDescendingMarker - 1
-	jsonFalseKeyDescendingMarker  = jsonNumberKeyDescendingMarker - 1
-	jsonTrueKeyDescendingMarker   = jsonFalseKeyDescendingMarker - 1
-	jsonArrayKeyDescendingMarker  = jsonTrueKeyDescendingMarker - 1
-	jsonObjectKeyDescendingMarker = jsonArrayKeyDescendingMarker - 1
+	jsonEmptyArrayKeyDescendingMarker = jsonObjectKeyMarker + 8
+	jsonNullKeyDescendingMarker       = jsonEmptyArrayKeyDescendingMarker - 1
+	jsonStringKeyDescendingMarker     = jsonNullKeyDescendingMarker - 1
+	jsonNumberKeyDescendingMarker     = jsonStringKeyDescendingMarker - 1
+	jsonFalseKeyDescendingMarker      = jsonNumberKeyDescendingMarker - 1
+	jsonTrueKeyDescendingMarker       = jsonFalseKeyDescendingMarker - 1
+	jsonArrayKeyDescendingMarker      = jsonTrueKeyDescendingMarker - 1
+	jsonObjectKeyDescendingMarker     = jsonArrayKeyDescendingMarker - 1
 
 	// Terminators for JSON Key encoding.
 	jsonKeyTerminator           byte = 0x00
@@ -1750,6 +1755,9 @@ const (
 	JSONArrayDesc  Type = 39
 	JSONObject     Type = 40
 	JSONObjectDesc Type = 41
+	// Special case
+	JsonEmptyArray     Type = 42
+	JsonEmptyArrayDesc Type = 43
 )
 
 // typMap maps an encoded type byte to a decoded Type. It's got 256 slots, one
@@ -1810,6 +1818,10 @@ func slowPeekType(b []byte) Type {
 			return JSONArray
 		case m == jsonArrayKeyDescendingMarker:
 			return JSONArrayDesc
+		case m == jsonEmptyArrayKeyMarker:
+			return JsonEmptyArray
+		case m == jsonEmptyArrayKeyDescendingMarker:
+			return JsonEmptyArrayDesc
 		case m == jsonObjectKeyMarker:
 			return JSONObject
 		case m == jsonObjectKeyDescendingMarker:
@@ -1970,7 +1982,8 @@ func PeekLength(b []byte) (int, error) {
 		length, err := getArrayOrJSONLength(b[1:], dir, IsJSONKeyDone)
 		return 1 + length, err
 	case jsonArrayKeyMarker, jsonArrayKeyDescendingMarker,
-		jsonObjectKeyMarker, jsonObjectKeyDescendingMarker:
+		jsonObjectKeyMarker, jsonObjectKeyDescendingMarker,
+		jsonEmptyArrayKeyMarker, jsonEmptyArrayKeyDescendingMarker:
 		dir := Ascending
 		if (m == jsonArrayKeyDescendingMarker) ||
 			(m == jsonObjectKeyDescendingMarker) {
@@ -3461,12 +3474,20 @@ func EncodeJSONTrueKeyMarker(buf []byte, dir Direction) []byte {
 
 // EncodeJSONArrayKeyMarker adds a JSON Array key encoding marker
 // to buf and returns the new buffer.
-func EncodeJSONArrayKeyMarker(buf []byte, dir Direction) []byte {
+func EncodeJSONArrayKeyMarker(buf []byte, dir Direction, length int64) []byte {
 	switch dir {
 	case Ascending:
-		return append(buf, jsonArrayKeyMarker)
+		if length == 0 {
+			return append(buf, jsonEmptyArrayKeyMarker)
+		} else {
+			return append(buf, jsonArrayKeyMarker)
+		}
 	case Descending:
-		return append(buf, jsonArrayKeyDescendingMarker)
+		if length == 0 {
+			return append(buf, jsonEmptyArrayKeyDescendingMarker)
+		} else {
+			return append(buf, jsonArrayKeyDescendingMarker)
+		}
 	default:
 		panic("invalid direction")
 	}
@@ -3582,15 +3603,15 @@ func ValidateAndConsumeJSONKeyMarker(buf []byte, dir Direction) ([]byte, Type, e
 	case Descending:
 		switch typ {
 		case JSONNullDesc, JSONNumberDesc, JSONStringDesc, JSONFalseDesc,
-			JSONTrueDesc, JSONArrayDesc, JSONObjectDesc:
+			JSONTrueDesc, JSONArrayDesc, JSONObjectDesc, JsonEmptyArrayDesc:
 			return buf[1:], typ, nil
 		default:
 			return nil, Unknown, errors.Newf("invalid type found %s", typ)
 		}
 	case Ascending:
 		switch typ {
 		case JSONNull, JSONNumber, JSONString, JSONFalse, JSONTrue, JSONArray,
-			JSONObject:
+			JSONObject, JsonEmptyArray:
 			return buf[1:], typ, nil
 		default:
 			return nil, Unknown, errors.Newf("invalid type found %s", typ)

pkg/util/json/json.go

@@ -1978,7 +1978,7 @@ func (j jsonTrue) EncodeForwardIndex(buf []byte, dir encoding.Direction) ([]byte
 }
 
 func (j jsonArray) EncodeForwardIndex(buf []byte, dir encoding.Direction) ([]byte, error) {
-	buf = encoding.EncodeJSONArrayKeyMarker(buf, dir)
+	buf = encoding.EncodeJSONArrayKeyMarker(buf, dir, int64(len(j)))
 	buf = encoding.EncodeJSONValueLength(buf, dir, int64(len(j)))
 
 	var err error