How to retrieve randomized data rows from a postgreSQL table?

Question

I have a table on a PostgreSQL server database with almost 3 million rows and I need to save all rows to a CSV file. The problem here is that the rows must be saved in a different random order each time I run the process.

Worth noting that it's a C# WinForms app.

I tried loading the data into a List<> and using a shuffling algorithm but it took forever to finish, and I realy need it to be fast. I think doing it directly in the query will be much faster but I don't have a clue on how to do it.

Stephan B · Accepted Answer · 2011-03-29 13:01:53Z

3

Typically, you can just ORDER BY a random function of your database flavor, like

SELECT * FROM table ORDER BY RANDOM()

This might be as slow as shuffling the list, depending on the database server or product.

answered Mar 29, 2011 at 13:01

Stephan B

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1 Comment

Henrique Miranda Over a year ago

It took 16 seconds to return the query, fairly acceptable and way faster than the shuffling. Thanks a lot.

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