选择具有较高价值而很少具有较低价值的行

Question

I'm trying to select a random row from a table, but there is a column in this table called Rate , I want it to return the row that has a higher rate, and rarely ever return the rows that has a lower rate, is this possible?

Table :

CREATE TABLE _Random (Code varchar(128), Rate tinyint)

Answer 1

So you want a random row, but weighted towards the ones with higher rates?

It would also be good to know how many rows there are in the table - sorting the whole lot is kinda expensive. You may prefer to use a row_number concept than sorting by N guids.

So... One option could be to generate a single number, and then divide 100 by it. Imagine we generate a number between 0 and 1.

.25 gives us 400, .5 gives us 200, .75 gives us 133... Notice that there's a curve here - so the numbers closer to 100 come up more often (subtract 100 to make the range start at 1).

You could use RAND() for a single value between 0 and 1 (it's probably good enough), and then do the division and subtraction to get a number. If this is higher than the count of records, then maybe repeat? But try to choose a value for your division that suits.

If you need to weight it more, you could raise your RAND() value by some number, to flatten it out or steepen it up. Do some experimenting to see how it looks.

Answer 2

This query will fetch a random record which has an above average rate

SELECT TOP (1) * FROM _Random 
WHERE Rate>(SELECT AVG(Rate) FROM _Random)
ORDER BY NEWID()