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.

score 3 · Accepted Answer · answered Mar 29 '11 at 13:01

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 '11 at 13:01

Stephan B

3,621
19
33

It took 16 seconds to return the query, fairly acceptable and way faster than the shuffling. Thanks a lot. – Henrique Miranda Mar 29 '11 at 13:12

score 2 · Answer 2 · edited May 23 '17 at 11:55

2

See this question Selecting random rows

See this wonderful link Depesz MY THOUGHTS ON GETTING RANDOM ROW

edited May 23 '17 at 11:55

Community

1
1

answered Mar 29 '11 at 14:02

Kuberchaun

27,671
6
47
57

How to retrieve randomized data rows from a postgreSQL table?

2 Answers2

Linked