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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4251b8cfb7c7fb2f85e9029d514066add37aca94a5445b85bd0d4d2843be9f0b' 
  AND token = '6ZiF3LKs0T4mDq2WRM2xowd8cUCeOM6+kk+zYZ/A27Q=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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