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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '31a9c6281cc11599fb5016270216408a1d1a5e00a7d28b285c218e267e4b1ef2' 
  AND token = 'dLKMWkk109AWFEUgfCPFa9UP4aC1F1VShbu/6AZez20=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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