How can I select 2 different random rows from a table?

问题

right now I have

row=session.query(Item).order_by(func.random()).limit(2)
name1=row[0].name
name2=row[1].name

Which gives me the first column(name) of each entry. The problem is, I get multiples (it will select the same random row twice. I want it to always be different. Is there a way to do this without an if, then statement?

if its useful, when I print row, it gives me something like this:

SELECT items.id AS items_id, items.name AS items_name, items.data AS items_data FROM items ORDER BY random() LIMIT ? OFFSET ?

why would it say limit ? I have put in limit(2)

回答1:

It seems that using order_by on func.random() is a bad idea in SQL (http://www.webtrenches.com/post.cfm/avoid-rand-in-mysql). Instead, I counted the length of the table, found 2 random numbers with in this length, and then queried the table to find the rows associated with these random numbers. Apparently this is faster. At least it doesn't have any repeats :)

number=session.query(func.count(Item.id)).scalar()
randoms=random.sample(range(number),2)
item1=session.query(Item).filter_by(id=randoms[0]+1).one()
item2=session.query(Item).filter_by(id=randoms[1]+1).one()

回答2:

SELECT items.id AS items_id, items.name AS items_name, items.data AS items_data
FROM items
ORDER BY random()
LIMIT 2;

Check the below link for reference.

http://www.tutorialspoint.com/sqlite/sqlite_limit_clause.htm

来源：https://stackoverflow.com/questions/19507467/how-can-i-select-2-different-random-rows-from-a-table