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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '878dd7f556b2b4fe7b4642ac288bcc8346f8edc5e0ff409fde7ce86fe90069a8' 
  AND token = '6/91jczxfXlRwIFp3tsUE8JgxCoPNXpBPUMabaqv/Is=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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