Best way to select random rows PostgreSQL

Question

I want a random selection of rows in PostgreSQL, I tried this:

select * from table where random() < 0.01;

But some other recommend this:

Answer 1

The one with the ORDER BY is going to be the slower one.

select * from table where random() < 0.01; goes record by record, and decides to randomly filter it or not. This is going to be O(N) because it only needs to check each record once.

select * from table order by random() limit 1000; is going to sort the entire table, then pick the first 1000. Aside from any voodoo magic behind the scenes, the order by is O(N * log N).

The downside to the random() < 0.01 one is that you'll get a variable number of output records.

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Note, there is a better way to shuffling a set of data than sorting by random: The Fisher-Yates Shuffle, which runs in O(N). Implementing the shuffle in SQL sounds like quite the challenge, though.