日付範囲を間隔の説明に変換する

最近のプロジェクトの要件は、リソースが完全に消費される時期を報告することでした。枯渇カレンダーの日付だけでなく、残り時間を「1年3か月」のように英語のような形式で表示するように求められました。

組み込みDATEDIFF関数

指定された開始日と終了日の間で交差する指定された日付部分の境界の数...を返します。

そのまま使用すると、誤解を招く、または紛らわしい結果が生じる可能性があります。たとえば、YEARの間隔を使用すると、1999-12-31（YYYY-MM-DD）と2000-01-01が1年離れていることが示されますが、これらの日付は1日だけ離れていると常識的に考えられます。逆に、DAY 1999-12-31と2010-12-31の間隔を使用すると、4,018日で区切られますが、ほとんどの人は「11年」をより適切に説明します。

日数から開始して、そこから月と年を計算すると、うるう年と月のサイズのエラーが発生しやすくなります。

これをさまざまなSQL方言でどのように実装できるのか疑問に思いました。出力例は次のとおりです。

create table TestData(
    FromDate date not null,
    ToDate date not null,
    ExpectedResult varchar(100) not null); -- exact formatting is unimportant

insert TestData (FromDate, ToDate, ExpectedResult)
values ('1999-12-31', '1999-12-31', '0 days'),
       ('1999-12-31', '2000-01-01', '1 day'),
       ('2000-01-01', '2000-02-01', '1 month'),
       ('2000-02-01', '2000-03-01', '1 month'),              -- month length not important
       ('2000-01-28', '2000-02-29', '1 month, 1 day'),       -- leap years to be accounted for
       ('2000-01-01', '2000-12-31', '11 months, 30 days'),
       ('2000-02-28', '2000-03-01', '2 days'),
       ('2001-02-28', '2001-03-01', '1 day'),                -- not a leap year
       ('2000-01-01', '2001-01-01', '1 year'),
       ('2000-01-01', '2011-01-01', '11 years'),
       ('9999-12-30', '9999-12-31', '1 day'),                -- catch overflow in date calculations
       ('1900-01-01', '9999-12-31', '8099 years 11 months 30 days');  -- min(date) to max(date)

私はたまたまSQL Server 2008R2を使用していますが、他の方言がこれをどのように処理するかを知りたいです。

次のソリューションはSQL Server用です。アプローチはに似てSergのクエリが唯一DATEADDおよびDATEDIFF機能を使用するには。ただし、負の間隔（FromDate > ToDate）は考慮されず、月の合計差から年と月が導出されます。

WITH
  MonthDiff AS
  (
    SELECT
      t.FromDate,
      t.ToDate,
      t.ExpectedResult,
      Months = x.Months - CASE WHEN DAY(t.FromDate) > DAY(t.ToDate) THEN 1 ELSE 0 END
    FROM
      dbo.TestData AS t
      CROSS APPLY (SELECT DATEDIFF(MONTH, t.FromDate, t.ToDate)) AS x (Months)
  )
SELECT
  t.FromDate,
  t.ToDate,
  t.ExpectedResult,
  Result = ISNULL(NULLIF(ISNULL(x.Years  + CASE x.Years  WHEN '1' THEN ' year '  ELSE ' years '  END, '')
                       + ISNULL(x.Months + CASE x.Months WHEN '1' THEN ' month ' ELSE ' months ' END, '')
                       + ISNULL(x.Days   + CASE x.Days   WHEN '1' THEN ' day '   ELSE ' days '   END, ''), ''), '0 days')
FROM
  MonthDiff AS t
  CROSS APPLY
  (
    SELECT
      CAST(NULLIF(t.Months / 12, 0) AS varchar(10)),
      CAST(NULLIF(t.Months % 12, 0) AS varchar(10)),
      CAST(NULLIF(DATEDIFF(DAY, DATEADD(MONTH, t.Months, t.FromDate), t.ToDate), 0) AS varchar(10))
  ) AS x (Years, Months, Days)
;

出力：

FromDate    ToDate      ExpectedResult                 Result
----------  ----------  -----------------------------  -----------------------------
1999-12-31  1999-12-31  0 days                         0 days
1999-12-31  2000-01-01  1 day                          1 day 
2000-01-01  2000-02-01  1 month                        1 month 
2000-02-01  2000-03-01  1 month                        1 month 
2000-01-28  2000-02-29  1 month, 1 day                 1 month 1 day 
2000-01-01  2000-12-31  11 months, 30 days             11 months 30 days 
2000-02-28  2000-03-01  2 days                         2 days 
2001-02-28  2001-03-01  1 day                          1 day 
2000-01-01  2001-01-01  1 year                         1 year 
2000-01-01  2011-01-01  11 years                       11 years 
9999-12-30  9999-12-31  1 day                          1 day 
1900-01-01  9999-12-31  8099 years 11 months 30 days   8099 years 11 months 30 days 

この回答は、SQL Server（2005+）CLR関数を使用した実装を示しています。

-- Enable CLR (if necessary)
EXECUTE sys.sp_configure 
    @configname = 'clr enabled',
    @configvalue = 1;

RECONFIGURE;

組み立てと機能

CREATE ASSEMBLY DBA
AUTHORIZATION dbo
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WITH PERMISSION_SET = SAFE;
GO
CREATE FUNCTION dbo.IntervalDescription
(
    @From date, 
    @To date
)
RETURNS nvarchar(100)
AS EXTERNAL NAME 
    DBA.UserDefinedFunctions.IntervalDescription;

使用法

SELECT 
    TD.FromDate,
    TD.ToDate,
    TD.ExpectedResult, 
    IntervalDescription = dbo.IntervalDescription(TD.FromDate, TD.ToDate) 
FROM dbo.TestData AS TD;

結果

ソース

_{私はC＃プログラマではありません！}

using Microsoft.SqlServer.Server;
using System;
using System.Text;

public partial class UserDefinedFunctions
{
    [SqlFunction
        (
        DataAccess = DataAccessKind.None,
        SystemDataAccess = SystemDataAccessKind.None,
        IsDeterministic = true,
        IsPrecise = true,
        Name = "IntervalDescription"
        )
    ]
    [return: SqlFacet(IsFixedLength = false, IsNullable = false, MaxSize = 100)]
    public static string IntervalDescription(DateTime From, DateTime To)
    {
        var workDate = From;
        int years = To.Year - From.Year;
        int months = 0;
        int days = 0;

        if (years != 0)
        {
            if (From.Month > To.Month || (From.Month == To.Month && From.Day > To.Day))
            {
                years--;
            }
            workDate = workDate.AddYears(years);
        }

        while (workDate < To && (workDate.Year != DateTime.MaxValue.Year || workDate.Month != DateTime.MaxValue.Month))
        {
            if (workDate.AddMonths(1) <= To)
            {
                months++;
                workDate = workDate.AddMonths(1);
            }
            else
            {
                break;
            }
        }

        while (workDate < To)
        {
            days++;
            workDate = workDate.AddDays(1);
        }

        StringBuilder sb = new StringBuilder(100);

        if (years > 0)
        {
            sb.Append(years);
            sb.Append(years == 1 ? " year" : " years");
            sb.Append((months > 0 || days > 0) ? ", " : string.Empty);
        }

        if (months > 0)
        {
            sb.Append(months);
            sb.Append(months == 1 ? " month" : " months");
            sb.Append(days > 0 ? ", " : string.Empty);
        }

        if (days > 0 || (years == 0 && months == 0))
        {
            sb.Append(days);
            sb.Append(days == 1 ? " day" : " days");
        }

        return
            sb.ToString();

    }
}

SQL Server 2008R2 SP2に実装されている私のバージョン。

CREATE FUNCTION dbo.ReadableInterval(
    @FromDate AS date,
    @ToDate AS date
)
RETURNS TABLE AS RETURN 
(
with YearStep as
(
    select
        max(n1.Number) as YearNumber
    from dbo.Numbers as n1
    where n1.Number <= DATEDIFF(YEAR, @FromDate, @ToDate)  -- see comment (A)
    and DATEADD(YEAR, n1.Number, @FromDate) <= @ToDate     -- see comment (B)
)
, MonthStep as
(
    select
        max(n2.Number) as MonthNumber
    from dbo.Numbers as n2
    cross apply YearStep as y1
    where n2.Number <= DATEDIFF(MONTH, DATEADD(YEAR, y1.YearNumber, @FromDate), @ToDate)
    and DATEADD(MONTH, n2.Number, DATEADD(YEAR, y1.YearNumber, @FromDate)) <= @ToDate
)
, DayStep as
(
    select
        DATEDIFF(day, DATEADD(MONTH, m1.MonthNumber, DATEADD(YEAR, y2.YearNumber, @FromDate)), @ToDate) as DayNumber
    from MonthStep as m1
    cross apply YearStep as y2
)
select
    y.YearNumber,
    m.MonthNumber,
    d.DayNumber
from YearStep as y
cross apply MonthStep as m
cross apply DayStep as d
)

与えられたテストデータで結果は

select
    td.FromDate,
    td.ToDate,
    td.ExpectedResult,
    ri.YearNumber as Years,
    ri.MonthNumber as Months,
    ri.DayNumber as [Days]
from dbo.TestData as td
cross apply dbo.ReadableInterval(td.FromDate, td.ToDate) as ri;

FromDate   ToDate     ExpectedResult               Years Months Days
---------- ---------- ---------------------------- ----- ------ ----
1999-12-31 1999-12-31 0 days                           0      0    0
1999-12-31 2000-01-01 1 day                            0      0    1
2000-01-01 2000-02-01 1 month                          0      1    0
2000-02-01 2000-03-01 1 month                          0      1    0
2000-01-28 2000-02-29 1 month, 1 day                   0      1    1
2000-01-01 2000-12-31 11 months, 30 days               0     11   30
2000-02-28 2000-03-01 2 days                           0      0    2
2001-02-28 2001-03-01 1 day                            0      0    1
2000-01-01 2001-01-01 1 year                           1      0    0
2000-01-01 2011-01-01 11 years                        11      0    0
9999-12-30 9999-12-31 1 day                            0      0    1
1900-01-01 9999-12-31 8099 years 11 months 30 days  8099     11   30

説明

私の一般的なアプローチは、最初の年から、次に月、次に日で、前の日付から一歩進むことです。細分度の各レベルでの目的は、終了日を超えずに終了日に近づき、次に低いレベルに進むことです。

私は数値表を使用して、「近くではなく近い」計算を容易にしています。この表からDATEADD、先行する最大の年/月/日の数を見つけることができますToDate-コード内のコメント（B）。

MAX番号を探していて、Numbersテーブルがクラスター化されているため、オプティマイザは降順スキャンを実行し、DATEADDに値を供給していました。Numbersには100,000を超える行が含まれるため、これにより日付オーバーフローエラーが発生していました。DATEADD(YEAR, 100000, @FromDate)9999-12-31より大きく、エラーが発生します。述語（A）は、日付のオーバーフローを回避して、逆方向スキャンを開始する数値の上限を指定します。その結果、クエリプランは、非常に大きな日付範囲であっても、ほとんど行を走査しません。

このアプローチは、年月を見つけるために使用されます。ただし、月の開始点は、最初のCTEで見つけた何年にもわたって進められます。DAYSは最小レベルの細分性なので、単純なDATEDIFFで十分です。

これは、必要に応じて間隔を時間、分、秒単位で返し、より細かい粒度に拡張できます。

PostgreSQLはageすぐに使用できる関数をサポートしています。

select
  FromDate,
  ToDate,
  ExpectedResult,
  age(ToDate, FromDate)
from TestData;

これにより、目的の結果が得られます。いくつかの追加の時間値を取得または取得します。

FromDate      ToDate        ExpectedResult                  age
----------    ----------    ----------------------------    --------------------------
1999-12-31    1999-12-31    0 days                          00:00:00
1999-12-31    2000-01-01    1 day                           1 day
2000-01-01    2000-02-01    1 month                         1 mon
2000-02-01    2000-03-01    1 month                         1 mon
2000-01-28    2000-02-29    1 month, 1 day                  1 mon 1 day
2000-01-01    2000-12-31    11 months, 30 days              11 mons 30 days
2000-02-28    2000-03-01    2 days                          2 days
2001-02-28    2001-03-01    1 day                           1 day
2000-01-01    2001-01-01    1 year                          1 year
2000-01-01    2011-01-01    11 years                        11 years
9999-12-30    9999-12-31    1 day                           1 day
1900-01-01    9999-12-31    8099 years 11 months 30 days    8099 years 11 mons 30 days

numberテーブルや集計が不要なバージョン。Michael Greenのテストデータで同じ結果が得られます。彼らはどこでデータで異なります @FromDate > @ToDate。 ReadableInterval2nullとは逆に負の値を返します。

CREATE FUNCTION dbo.ReadableInterval2(
    @FromDate AS date,
    @ToDate AS date
)
RETURNS TABLE AS RETURN 
(with checkData as (
    select 
       fromDate = case when @FromDate > @ToDate then @ToDate else @FromDate end,
       toDate = case when @FromDate <= @ToDate then @ToDate else @FromDate end,
       k = case when @FromDate > @ToDate then -1 else 1 end
), MonthStep as (
    select k, FromDate, ToDate,
        YearNumber = x.months / 12,
        MonthNumber = x.months % 12
    from checkdata
    cross apply(
        select months = DATEDIFF(MONTH, FromDate, ToDate)
            - case when DAY(FromDate) > DAY(ToDate) then 1 else 0 end
        ) x
)
select YearNumber = k*YearNumber, 
      MonthNumber = k*MonthNumber,
      DayNumber = k*DATEDIFF(day, DATEADD(MONTH, MonthNumber, DATEADD(YEAR, YearNumber, FromDate)), ToDate) 
    from MonthStep 
)