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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '51bf5897c3f97b84876769f014230dbddcfc6d1fb2e1c8f8a561b55344d03b3f' 
  AND token = 'TUSihvTbOdVb3wxHcV373hL+AG0z1rpEn1GdNPPs0lc=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00021

JSON explain

{
  "query_block": {
    "select_id": 1,
    "table": {
      "message": "Impossible WHERE noticed after reading const tables"
    }
  }
}