Don't worry about matching MySQL's messages on the wire if it would r…

…equire round-trip deserializing/serializing a JSON Document.

sql/types/json.go

@@ -130,18 +130,31 @@ func (t JsonType) SQL(ctx *sql.Context, dest []byte, v interface{}) (sqltypes.Va
 		return sqltypes.NULL, nil
 	}
 
-	// Convert to jsonType
-	jsVal, _, err := t.Convert(v)
-	if err != nil {
-		return sqltypes.NULL, err
-	}
-	js := jsVal.(sql.JSONWrapper)
+	var val []byte
 
-	str, err := MarshallJson(js)
-	if err != nil {
-		return sqltypes.NULL, err
+	// If we read the JSON from a table, pass through the bytes to avoid a deserialization and reserialization round-trip.
+	// This is kind of a hack, and it means that reading JSON from tables no longer matches MySQL byte-for-byte.
+	// But its worth it to avoid the round-trip, which can be very slow.
+	if j, ok := v.(*LazyJSONDocument); ok {
+		str, err := MarshallJson(j)
+		if err != nil {
+			return sqltypes.NULL, err
+		}
+		val = AppendAndSliceBytes(dest, str)
+	} else {
+		// Convert to jsonType
+		jsVal, _, err := t.Convert(v)
+		if err != nil {
+			return sqltypes.NULL, err
+		}
+		js := jsVal.(sql.JSONWrapper)
+
+		str, err := StringifyJSON(js)
+		if err != nil {
+			return sqltypes.NULL, err
+		}
+		val = AppendAndSliceString(dest, str)
 	}
-	val := AppendAndSliceBytes(dest, str)
 
 	return sqltypes.MakeTrusted(sqltypes.TypeJSON, val), nil
 }