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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a251f6dc645a0785ec57f5dd1cfe2880ae346db8b99b97debfc1c96d009a2554' 
  AND token = 'B6XB6EAEgjEmfLRwZ2FE0DnXZA3dxrIVCWnBmV75nwI=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00031

JSON explain

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