如何根据条件在SQL中创建行？

Question

SQL中是否可以根据前一个月的值创建行？

我们正在按季度跟踪指标，因此1月的实际值与2月和3月的实际值相同。

在SQL中执行此操作的最佳方法是什么？

Answer 1

使用“从选择插入”：

insert into mytable (month, column1, column2)
select 'feb', column1, column2 from mytable where month='jan'

insert into mytable (month, column1, column2)
select 'mar', column1, column2 from mytable where month='jan'

列出您要复制的所有列。

Answer 2

由于以下原因，这个问题很难回答：

1. 请标记您正在使用的引擎。 没有一个引擎完全符合SQL标准，特别是当它适用于日期/时间操作时。
2. 您的数据时间戳是每日，每周还是每月数据？
3. 您可以提供一些DDL和预期的输出吗？

做好了整理工作后，假设您拥有每日数据。 我从Yahoo Finance获取了AAPL的一些股价数据。 我提供了一个查询示例，该查询提供了前一个季度的平均收盘价数据。 使用PostgreSQL语法。 注意：在其他引擎（例如Oracle，请参见： ADD_MONTHS ）或SQL Server下，此语法将有所不同。

SELECT 
  p.trading_date,
  EXTRACT(QUARTER FROM p.trading_date) current_quarter,
  EXTRACT(MONTH FROM p.trading_date) current_month,
  EXTRACT(QUARTER FROM p.trading_date - INTERVAL '3 MONTHS') last_quarter,
  EXTRACT(YEAR FROM p.trading_date - INTERVAL '3 MONTHS') last_quarter_year,
  (
     SELECT AVG(p2.close_price)
     FROM price_data p2
     WHERE 1 = 1
      AND EXTRACT(QUARTER FROM p2.trading_date) = EXTRACT(QUARTER FROM p.trading_date - INTERVAL '3 MONTHS')
      AND EXTRACT(YEAR FROM p2.trading_date) = EXTRACT(YEAR FROM p.trading_date - INTERVAL '3 MONTHS')
  ) average_close_price_last_quarter,
  p.close_price
FROM price_data p;

创建表price_data（trading_date DATE NOT NULL，标记VARCHAR（50），close_price numeric（10，2））;

每日数据的示例DDL：

INSERT INTO price_data (trading_date, close_price) VALUES 
('2017-07-10',142.84),
('2017-07-12',143.509186),
('2017-07-13',145.508102),
('2017-07-14',146.758636),
('2017-07-17',147.270706),
('2017-07-18',147.782761),
('2017-07-19',148.708359),
('2017-07-20',148.038757),
('2017-07-21',147.969849),
('2017-07-24',149.761978),
('2017-07-25',150.402039),
('2017-07-26',151.111023),
('2017-07-27',148.255402),
('2017-07-28',147.211624),
('2017-07-31',146.4534),
('2017-08-01',147.753204),
('2017-08-02',154.734665),
('2017-08-03',153.188705),
('2017-08-04',153.99614),
('2017-08-07',156.37912),
('2017-08-08',157.629684),
('2017-08-09',158.594666),
('2017-08-10',153.543152),
('2017-08-11',155.678436),
('2017-08-14',158.021317),
('2017-08-15',159.751297),
('2017-08-16',159.108719),
('2017-08-17',156.054092),
('2017-08-18',155.698212),
('2017-08-21',155.41153),
('2017-08-22',157.952118),
('2017-08-23',158.149826),
('2017-08-24',157.447952),
('2017-08-25',158.031189),
('2017-08-28',159.622787),
('2017-08-29',161.046326),
('2017-08-30',161.481277),
('2017-08-31',162.12384),
('2017-09-01',162.173279),
('2017-09-05',160.225815),
('2017-09-06',160.057755),
('2017-09-07',159.415192),
('2017-09-08',156.815277),
('2017-09-11',159.652451),
('2017-09-12',159.01976),
('2017-09-13',157.823593),
('2017-09-14',156.469269),
('2017-09-15',158.050964),
('2017-09-18',156.854813),
('2017-09-19',156.914124),
('2017-09-20',154.284561),
('2017-09-21',151.635208),
('2017-09-22',150.15239),
('2017-09-25',148.827698),
('2017-09-26',151.388062),
('2017-09-27',152.465607),
('2017-09-28',151.526474),
('2017-09-29',152.356857),
('2017-10-02',152.050415),
('2017-10-03',152.712738),
('2017-10-04',151.724197),
('2017-10-05',153.612335),
('2017-10-06',153.523361),
('2017-10-09',154.057175),
('2017-10-10',154.116486),
('2017-10-11',154.759079),
('2017-10-12',154.215363),
('2017-10-13',155.194031),
('2017-10-16',158.050964),
('2017-10-17',158.634216),
('2017-10-18',157.932343),
('2017-10-19',154.195572),
('2017-10-20',154.462494),
('2017-10-23',154.383408),
('2017-10-24',155.302765),
('2017-10-25',154.620682),
('2017-10-26',155.609222),
('2017-10-27',161.184708),
('2017-10-30',164.812729),
('2017-10-31',167.106186),
('2017-11-01',164.980774),
('2017-11-02',166.186829),
('2017-11-03',170.526596),
('2017-11-06',172.256577),
('2017-11-07',172.810165),
('2017-11-08',174.223831),
('2017-11-09',173.86795),
('2017-11-10',173.292511),
('2017-11-13',172.598022),
('2017-11-14',169.988754),
('2017-11-15',167.746582),
('2017-11-16',169.750671),
('2017-11-17',168.808151),
('2017-11-20',168.639496),
('2017-11-21',171.774567),
('2017-11-22',173.580231),
('2017-11-24',173.590149),
('2017-11-27',172.717072),
('2017-11-28',171.705139),
('2017-11-29',168.143433),
('2017-11-30',170.494751),
('2017-12-01',169.70105),
('2017-12-04',168.460922),
('2017-12-05',168.30217),
('2017-12-06',167.677139),
('2017-12-07',167.984711),
('2017-12-08',168.034302),
('2017-12-11',171.308289),
('2017-12-12',170.345932),
('2017-12-13',170.911438),
('2017-12-14',170.861832),
('2017-12-15',172.598022),
('2017-12-18',175.028717),
('2017-12-19',173.163528),
('2017-12-20',172.975037),
('2017-12-21',173.629822),
('2017-12-22',173.629822),
('2017-12-26',169.224838),
('2017-12-27',169.254608),
('2017-12-28',169.73082),
('2017-12-29',167.895416),
('2018-01-02',170.901505),
('2018-01-03',170.871735),
('2018-01-04',171.665436),
('2018-01-05',173.619904),
('2018-01-08',172.975037),
('2018-01-09',172.9552),
('2018-01-10',172.915497),
('2018-01-11',173.897705),
('2018-01-12',175.69342),
('2018-01-16',174.800537),
('2018-01-17',177.687576),
('2018-01-18',177.846313),
('2018-01-19',177.052628),
('2018-01-22',175.604141),
('2018-01-23',175.643814),
('2018-01-24',172.846054),
('2018-01-25',169.760574),
('2018-01-26',170.157425),
('2018-01-29',166.635422),
('2018-01-30',165.653244),
('2018-01-31',166.109604),
('2018-02-01',166.456848),
('2018-02-02',159.234253),
('2018-02-05',155.25589),
('2018-02-06',161.744293),
('2018-02-07',158.281815),
('2018-02-08',153.926437),
('2018-02-09',155.809189),
('2018-02-12',162.084991),
('2018-02-13',163.708725),
('2018-02-14',166.727081),
('2018-02-15',172.3255),
('2018-02-16',171.767639),
('2018-02-20',171.18988),
('2018-02-21',170.412872),
('2018-02-22',171.837372),
('2018-02-23',174.825851),
('2018-02-26',178.282532),
('2018-02-27',177.704758),
('2018-02-28',177.435791),
('2018-03-01',174.327774),
('2018-03-02',175.533142),
('2018-03-05',176.140793),
('2018-03-06',175.991364),
('2018-03-07',174.357666),
('2018-03-08',176.26033),
('2018-03-09',179.288635),
('2018-03-12',181.021957),
('2018-03-13',179.278687),
('2018-03-14',177.754562),
('2018-03-15',177.963745),
('2018-03-16',177.336182),
('2018-03-19',174.626633),
('2018-03-20',174.566864),
('2018-03-21',170.612106),
('2018-03-22',168.201401),
('2018-03-23',164.306427),
('2018-03-26',172.106354),
('2018-03-27',167.693359),
('2018-03-28',165.8405),
('2018-03-29',167.135513),
('2018-04-02',166.039734),
('2018-04-03',167.743164),
('2018-04-04',170.950806),
('2018-04-05',172.13623),
('2018-04-06',167.733215),
('2018-04-09',169.39679),
('2018-04-10',172.584503),
('2018-04-11',171.777618),
('2018-04-12',173.471085),
('2018-04-13',174.058807),
('2018-04-16',175.144638),
('2018-04-17',177.555328),
('2018-04-18',177.15686),
('2018-04-19',172.13623),
('2018-04-20',165.08342),
('2018-04-23',164.60527),
('2018-04-24',162.314102),
('2018-04-25',163.021362),
('2018-04-26',163.589188),
('2018-04-27',161.696487),
('2018-04-30',164.625183),
('2018-05-01',168.450439),
('2018-05-02',175.891754),
('2018-05-03',176.21051),
('2018-05-04',183.123856),
('2018-05-07',184.448746),
('2018-05-08',185.335327),
('2018-05-09',186.640305),
('2018-05-10',189.309998),
('2018-05-11',188.589996),
('2018-05-14',188.149994),
('2018-05-15',186.440002),
('2018-05-16',188.179993),
('2018-05-17',186.990005),
('2018-05-18',186.309998),
('2018-05-21',187.630005),
('2018-05-22',187.160004),
('2018-05-23',188.360001),
('2018-05-24',188.149994),
('2018-05-25',188.580002),
('2018-05-29',187.899994),
('2018-05-30',187.5),
('2018-05-31',186.869995),
('2018-06-01',190.240005),
('2018-06-04',191.830002),
('2018-06-05',193.309998),
('2018-06-06',193.979996),
('2018-06-07',193.460007),
('2018-06-08',191.699997),
('2018-06-11',191.229996),
('2018-06-12',192.279999),
('2018-06-13',190.699997),
('2018-06-14',190.800003),
('2018-06-15',188.839996),
('2018-06-18',188.740005),
('2018-06-19',185.690002),
('2018-06-20',186.5),
('2018-06-21',185.460007),
('2018-06-22',184.919998),
('2018-06-25',182.169998),
('2018-06-26',184.429993),
('2018-06-27',184.160004),
('2018-06-28',185.5),
('2018-06-29',185.110001),
('2018-07-02',187.179993),
('2018-07-03',183.919998),
('2018-07-05',185.399994),
('2018-07-06',187.970001),
('2018-07-09',190.580002),
('2018-07-10',190.350006);