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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '4ab40c803cfd70d481c06138d17ff863e1bbffcd1dc2f6100e617d3aec67f124' 
  AND token = '5njKDr0dg+pED0w7mpEJly7PRmxdzVUCie0XApo7EtU=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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