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SELECT 
  1 
FROM 
  cscart_aprillock_keys 
WHERE 
  key_id = '1478cb7f55bcc3ef54e87c638e4c551940d5fcee31ab0c8dd2fa6c94f765cf8f' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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