This is the table structure and it only contains these two rows:

```
--------------------------
|id   | item  | priority |
--------------------------
|1    | item1 | 20       |
--------------------------
|2    | item2 | 30       |
--------------------------

```

I have to write a query on the table to get any of these 2 rows or nothing by percentage of chance.

20% chance to get item1

30% chance to get item2

50% chance to get nothing