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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'b8bb75f8ef729f511489ed7d5ac1bc3b0e716d5c031c675bca2e19e76e0338ca' 
  AND token = 'RR+tDJ1BXaISZmw4PnFtzaREeYCdK8FG5nbmKMgqMjQ=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00018

JSON explain

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