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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6a643a36d41ebc99592407cb4b16997b5dcac491637c8af6901972453fa3876a' 
  AND token = 'rQTAs4jz9SvbeSdvTVKtYM3fIoB9dcXSpsP4qdn//20=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}