How can I generate a series of repeating numbers in PostgreSQL?

问题

In PostgreSQL, is it possible to generate a series of repeating numbers? For example, I want to generate the numbers 1 to 10, with each number repeated 3 times:

1
1
1
2
2
2
3
3
3
.. and so on.

回答1:

You could cross join it to a series of 3:

SELECT a.n
from generate_series(1, 100) as a(n), generate_series(1, 3)

回答2:

You could try integer division like this:

SELECT generate_series(3, 100) / 3

回答3:

For such small numbers CROSS JOIN two VALUES expressions:

SELECT n
FROM  (VALUES (1),(2),(3)) x(r)  -- repetitions (values are not used)
     ,(VALUES (1),(2),(3),(4),(5),(6),(7),(8),(9),(10)) y(n); -- numbers

SQL Fiddle.

This works for any sequence of numbers (including repeated or irregular patterns).
For anything bigger and with regular sequential pattern use generate_series() as has been suggested.

回答4:

SELECT * FROM (SELECT generate_series(1, 10)) A
JOIN (
  SELECT generate_series(1, 3)
) B ON (TRUE)

http://www.sqlfiddle.com/#!12/d41d8

回答5:

I don't know if you can do use generate_series like that in PostgreSQL, but i would try a cross join:

SELECT x FROM
  (SELECT generate_series(1, 10) AS x) t1, 
  (SELECT generate_series(1, 3) as y) t2

Edit:

As generate_series already returns a table there's no need for SELECT in a Derived Table:

SELECT x FROM
  generate_series(1, 10) AS x, 
  generate_series(1, 3) as y

回答6:

Just another options:

select generate_series(1, 3) from generate_series(1, 10)

select generate_series(1, 30) % 10 + 1

回答7:

SELECT a.x from generate_series(0, 100) as a(x), generate_series(1, 3)

来源：https://stackoverflow.com/questions/23358333/how-can-i-generate-a-series-of-repeating-numbers-in-postgresql

标签

sql

postgresql

generate-series