Random Sampling in Google BigQuery

Question

I just discovered that the RAND() function, while undocumented, works in BigQuery. I was able to generate a (seemingly) random sample of 10 words from the Shakespeare dataset using:

SELECT word FROM

(SELECT rand() as random,word FROM [publicdata:samples.shakespeare] ORDER BY random)

LIMIT 10

 My question is: Are there any disadvantages to using this approach instead of the HASH() method defined in the "Advanced examples" section of the reference manual? https://developers.google.com/bigquery/query-reference

Answer 1

RAND() function can be used to generate a (seemingly) random number. You can use it to fetch a sample of 10 words from the Shakespeare dataset using:

#standardSQL

SELECT word

FROM `publicdata.samples.shakespeare`

WHERE RAND() < 10/164656

or even better:

#standardSQL

SELECT word

FROM `publicdata.samples.shakespeare`

WHERE RAND() < 10/(SELECT COUNT(*) FROM `publicdata.samples.shakespeare`) 

(where 10 is the approximate number of results I want to get, and 164656 the number of rows that table has)