季度的通用结束日期，PostgreSQL

Question

我想生成给定日期的通用季度结束日期。

例如：如果我有2010-01-01，我想返回2010-03-31，等等。

我可以得到季度号和年份：

select to_char(date_trunc('quarter',  current_date)::date, 'yyyy-q');

2017-3从今天起返回的是2017-07-14

我如何很好地获得季度结束日期？

我可以得到答案，但它非常丑陋：

select to_char(date_trunc('year',  date '2015-01-01'),'yyyy') || '-' ||case
    when (select extract('quarter' from date_trunc('quarter', date '2015-01-01')::date )) = 1 then '03-31'
    when (select extract('quarter' from date_trunc('quarter', date '2015-01-01')::date )) = 2 then '06-30'
    when (select extract('quarter' from date_trunc('quarter', date '2015-01-01')::date )) = 3 then '09-30'
    when (select extract('quarter' from date_trunc('quarter', date '2015-01-01')::date )) = 4 then '12-31'
    else '?'
    end 

返回2015-03-31因为我把2015-01-01。

有没有更好的办法？

Answer 1

我认为解决这个问题的最短和最优雅的方法是使用date_trunc('quarter',d)（将检索季度的开始）+ 3 个月 - 1 天，并使用表达式创建一个FUNCTION：

CREATE FUNCTION end_of_quarter (d date) 
RETURNS date AS
$$
SELECT
    CAST(date_trunc('quarter', d)  + interval '3 months' - interval '1 day' AS date)
$$
LANGUAGE SQL IMMUTABLE ;

...然后使用它：

SELECT
    d, end_of_quarter(d)
FROM
    (SELECT 
        CAST(d0 AS date) AS d 
    FROM 
        generate_series(date '2017-01-01', date '2017-12-31', interval '6 days') AS s(d0)
    ) AS q ;

d | 季末
:---------- | :-------------
2017-01-01 | 2017-03-31    
...
2017-03-26 | 2017-03-31    
2017-04-01 | 2017-06-30    
...
2017-06-18 | 2017-06-30    
2017-07-06 | 2017-09-30    
2017-07-12 | 2017-09-30    
...   
2017-09-22 | 2017-09-30    
2017-09-28 | 2017-09-30    
2017-10-04 | 2017-12-31    
2017-10-10 | 2017-12-31    
...  
2017-12-21 | 2017-12-31    
2017-12-27 | 2017-12-31    

您可以在此处的dbfiddle 中查看

您还可以通过使用以下简单版本来缩短您的原始方法CASE expression WHEN value THEN ...：

SELECT
    d, 
    extract('year' from d) || '-' ||
    /* case expression when value instead of case when expression */
    case extract('quarter' from d)
        when 1 then '03-31'
        when 2 then '06-30'
        when 3 then '09-30'
        else        '12-31'
    end AS end_of_quarter
FROM
    generate_series(date '2017-01-01', date '2017-12-31', interval '6 days') AS s(d) ;

您可以在此处的dbfiddle 中查看

如果您需要经常这样做，请定义一个函数：

CREATE FUNCTION end_of_quarter (d date) 
RETURNS date AS
$$
SELECT
    cast (extract('year' from d) || '-' ||
        case extract('quarter' from d)
            when 1 then '03-31'
            when 2 then '06-30'
            when 3 then '09-30'
            else        '12-31'
        end
    AS date)
$$
LANGUAGE SQL IMMUTABLE ;

dbfiddle在这里