How to generate a virtual table to generate a sequence of dates in PostgreSQL?

Question

I'd like to generate a list of dates with the hopes of joining with another table, but I don't know what syntax to use, something similar to this:

SELECT dates.date, transactions.account_id, transactions.amount
  FROM (...) as dates
       LEFT JOIN transactions ON transactions.date = dates.date
 WHERE dates.date >= '2010-01-01' AND dates.date <= '2010-12-31'
 ORDER BY dates.date;

I want the dates so I don't have to further massage the data client-side. I'm using this to display a table similar to this:

Account    2010-01-01    2010-01-02    2010-01-03    Balance
============================================================
Chase 123        +100           -20           -70        +10
Chase 231                       +13            -9         +4

OMG Ponies · Accepted Answer · 2010-10-23 01:52:09Z

12

List of Dates

Use the generate_series function to get a list of numbers that you can add to a date in order to get a list of dates:

SELECT CURRENT_DATE + s.a AS dates 
  FROM generate_series(0,14,7) as s(a);

Result:

dates
------------
2004-02-05
2004-02-12
2004-02-19

Pivoting

The latter part of your question deals with pivoting the result set -- converting row data into columnar data. PIVOT and UNPIVOT are ANSI, but I don't see them as supported by PostgreSQL currently. The most consistently supported means of pivoting a query is to use aggregate functions:

   SELECT t.account,
          SUM(CASE WHEN t.date = '2010-01-01' THEN t.amount END) AS '2010-01-01',
          SUM(CASE WHEN t.date = '2010-01-02' THEN t.amount END) AS '2010-01-02',
          SUM(CASE WHEN t.date = '2010-01-03' THEN t.amount END) AS '2010-01-03',
          SUM(t.amount) AS Balance
     FROM (SELECT CURRENT_DATE + s.a AS dates 
             FROM generate_series(0,14,7) as s(a)) x
LEFT JOIN TRANSACTIONS y ON y.date = x.date
 GROUP BY t.account

Dynamic Columns

...means dynamic SQL.

answered Oct 23, 2010 at 1:52

OMG Ponies

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3 Comments

Kuberchaun Over a year ago

What abou using the crosstab function to pivot? postgresql.org/docs/current/static/tablefunc.html

OMG Ponies Over a year ago

@StarShip3000: Yes, but it's not ANSI

Kuberchaun Over a year ago

From the best I can find PIVOT and UNPIVOT aren't part of ANSI as of sql-2003. Can you point me to a place that says otherwise? I used savage.net.au/SQL as a place to look.

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