Apex domains cannot have CNAME records.
Question and response
Question
dig sqldb.us. NS
Answer
sqldb.us. 5 NS dns.sqldb.us.
sqldb.us. 5 NS dns1.sqldb.us.
sqldb.us. 5 NS dns2.sqldb.us.
Authority
The response has no authority records.
Additional
dns.sqldb.us. 5 A 82.29.128.43
dns1.sqldb.us. 5 A 103.124.104.139
dns2.sqldb.us. 5 A 103.124.105.192
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0