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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = '6b4ba95d2cb05ac916f7dba0a4d8b298c48f2f1d2f1a7e4bb41f302b63855743' 
  AND token = 'PiQcqMsJcj0Px/H3WdO1tmJQ1WM9dU3blMErS4IqmS4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00027

JSON explain

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