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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b508fc6b8cd287eff0c46623ce75a0681bd612fadf770cbff1596c4501af2f78' 
  AND token = 'hQWApvbj41TwPWpBW0DqS2mEQKOxNbJYvMIWfoxJqG4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

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