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SELECT 
  1 
FROM 
  cscart_aprillock_keys 
WHERE 
  key_id = 'ff21517fdac3c63718f6b35750dbad33fd40112d26482c2d6069da9c2bdc8b48' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00029

JSON explain

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