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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '21d6355b3465f49c24348a2defc988922f7bca7e92f78503d0ff9623e9ea6da7' 
  AND token = 'VCE9gvES7l25d+/sYvsPR3+CcxCmloMxXsf9bqkYG6s=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00022

JSON explain

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