sql - 如何生成虚拟表以在 PostgreSQL 中生成日期序列？

Question

我想生成一个日期列表，希望与另一个表连接，但我不知道要使用什么语法，类似于这样:

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;

我想要日期，这样我就不必在客户端进一步处理数据了。我正在使用它来显示与此类似的表格:

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

Answer 1

日期列表

使用 generate_series function获取可以添加到日期以获取日期列表的数字列表:

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

结果:

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

旋转

问题的后半部分涉及对结果集进行透视——将行数据转换为列数据。 PIVOT 和 UNPIVOT 是 ANSI，但我不认为它们是 supported by PostgreSQL currently .最一致支持的旋转查询的方法是使用聚合函数:

   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

动态列

...表示dynamic SQL .