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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'a76dfdfa7063184169443b50c7717fd906a4691cfd7bdee0f525a42afd05f68d' 
  AND token = '8k8nqufr18WL8O5rhN6exQc5nbQSXTV1HEfhxZohTGY=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00034

JSON explain

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