support basic json filtering and selection

weed/query/json/seralize.go

@@ -0,0 +1,17 @@
+package json
+
+import "github.com/chrislusf/seaweedfs/weed/query/sqltypes"
+
+func ToJson(buf []byte, selections []string, values []sqltypes.Value) []byte {
+	buf = append(buf, '{')
+	for i, value := range values {
+		if i > 0 {
+			buf = append(buf, ',')
+		}
+		buf = append(buf, selections[i]...)
+		buf = append(buf, ':')
+		buf = append(buf, value.Raw()...)
+	}
+	buf = append(buf, '}')
+	return buf
+}