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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c261a90295919af415651a595d65edb98edc15c1d79484807d75ff305948c69f' 
  AND token = '12trHMfrg4+rYeZ6EjuE4VZ4klwzJs/sI5MdBjGfzHA=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00039

JSON explain

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