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8

The second suggestion is not random. You can't predict the row that's going to be picked, but if you had to bet, you'd bet on the second row. And you'd never bet on the last row, it's the less likely to be picked whatever is the distribution of your num_value and how big your table is.
– Etienne Racine
Commented Nov 14, 2010 at 17:38
1

I know that usually RAND() functions are not of very high quality, but other than that can you please elaborate why the selection wouldn't be random?
– Grey Panther
Commented Nov 16, 2010 at 11:43
13

The first one is WRONG in SQL Server. The RAND() function is invoked only once per query not once per row. So it always selects the first row (try it).
– Jeff Walker Code Ranger
Commented Feb 8, 2012 at 21:49
3

The second one also assumes that all of the rows are accounted for: it's possible it will choose a row that has been deleted.
– Sam Rueby
Commented Feb 20, 2012 at 13:56
3

@Sam.Rueby Actually, num_value >= RAND() ... limit 1 ensures that empty rows will be skipped until it finds exisiting row.
– ghord
Commented Jul 22, 2012 at 13:51

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