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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51ad51e04405c592b9513b18b875421ff557915886155fb503dc004a2739ca9f' 
  AND token = 'S6wn4alHMZtsqg2KQJg6JxY2f94mjyooFbKvRrXFMMU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00028

JSON explain

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