How to change the series of zeroes in a computed column

问题

I am using the below T-SQL to create a table with a computed column which gives me IDs in 'BID(The Year)-0000'. The issue is that I would like to reset the series of zeros in the ID when the year is changed.For example, the last ID in the table is BID2017-0923 when the year is changed I want the series to be reset for example 'BID2018-0001'.

Here is the T-SQL which currently I am using.

CREATE TABLE Books
(
    ID INT IDENTITY(1,1) NOT NULL PRIMARY KEY,
    IDCreateDate DATETIME NOT NULL DEFAULT GETDATE(),
    BookID AS ('BID' + LTRIM(YEAR(IDCreateDate)) + '-' + RIGHT('0000' + LTRIM(ID), 4)),
    ISBN VARCHAR(32),
    BookName NVARCHAR(50),
    AuthorName NVARCHAR(50),
    BLanguage VARCHAR(50),
    StaId int,
    StuId int,
    CatNo int
);

UPDATE: Furthermore, I would like the ID col to remembers its last id based on the year it has.For example, the last id in the column is BID2017-0920 when I change the year to 2010, it has to reset the number series for example BID2010-0001 but when I switch back the year to 2017, I don't want the series to be reset rather I want it to start from BID2017-0921.

回答1:

Edit#1: I've updated my solution according to latest OP's comments

/*
CREATE TABLE dbo.CustomSequence (
    Name VARCHAR(50) NOT NULL,
    Prefix      VARCHAR(10) NOT NULL,
    LastValue   VARCHAR(50) NULL, -- All generated values will have following pattern: PrefixYYYY-SeqvNumber
    LastYear    SMALLINT NOT NULL,
        CONSTRAINT PK_CustomSequence_Name_LastYear PRIMARY KEY (Name, LastYear),
    LastNumber  SMALLINT NULL
);
GO
-- Config OrderSequence 2014
INSERT  dbo.CustomSequence (Name, Prefix, LastValue, LastYear, LastNumber) 
VALUES  ('BookSequence', 'BID', NULL, 2014, 1)
GO
-- Config OrderSequence 2017
INSERT  dbo.CustomSequence (Name, Prefix, LastValue, LastYear, LastNumber) 
VALUES  ('BookSequence', 'BID', NULL, 2017, 1)
GO
*/

-- Generating new seq
    -- IN Parameters
    DECLARE @CustomSequenceName VARCHAR(50) = 'BookSequence'
    DECLARE @Year               SMALLINT = 2017 --YEAR(GETDATE())
    DECLARE @LenOfNumber        TINYINT = 4
    -- End of IN Parameters
    -- OUT Parameters
    DECLARE @GeneratedValue     VARCHAR(50)
    -- End of OUT Parameters

    UPDATE  s
    SET     LastNumber      = IIF(LastValue IS NULL, LastNumber, LastNumber + 1) + IIF(LastNumber = REPLICATE('9', @LenOfNumber), 1/0, 0),
            @GeneratedValue = LastValue = Prefix + LTRIM(@Year) + '-' + RIGHT(REPLICATE('0', @LenOfNumber)  + LTRIM(IIF(LastValue IS NULL, LastNumber, LastNumber + 1)), @LenOfNumber)
    FROM    dbo.CustomSequence s
    WHERE   s.Name = @CustomSequenceName
    AND     s.LastYear = @Year
-- End of Generating new seq

SELECT @GeneratedValue
SELECT * FROM dbo.CustomSequence
--> BID2017-0001, BID2017-0002, BID2017-0003, ...

Note#1: This solution work with pessimistic concurrency control (default behavior of SQL Server Database Engine)

Note#2: If we are reaching 10000 following piece of code

... IIF(LastNumber = 9999, 1/0, 0) ...

will raise an exception

Msg 8134, Level 16, State 1, Line 30
Divide by zero error encountered.
The statement has been terminated.

Note#3: UPDATE statement could be encapsulated into a stored procedure with @CustomSequenceName VARCHAR(50) as input parameter and @GeneratedValue VARCHAR(50) OUTPUT as OUT[PUT] parameter.

Note#4: @LenOfNumber allows to customize length of sequential number (default is 4)

Edit#2:

UPDATE statement could be replaced with following combination of INSERT + UPDATE statements:

SET XACT_ABORT ON
BEGIN TRAN
    IF NOT EXISTS(SELECT * FROM dbo.CustomSequence s WITH(HOLDLOCK) WHERE s.Name = @CustomSequenceName AND s.LastYear = @Year)
    BEGIN
        INSERT  dbo.CustomSequence (Name, Prefix, LastValue, LastYear, LastNumber) 
        VALUES  (@CustomSequenceName, @Prefix, NULL, @Year, 1)
    END
    UPDATE  s
    SET     LastNumber      = IIF(LastValue IS NULL, LastNumber, LastNumber + 1) + IIF(LastNumber = REPLICATE('9', @LenOfNumber), 1/0, 0),
            @GeneratedValue = LastValue = Prefix + LTRIM(@Year) + '-' + RIGHT(REPLICATE('0', @LenOfNumber)  + LTRIM(IIF(LastValue IS NULL, LastNumber, LastNumber + 1)), @LenOfNumber)
    FROM    dbo.CustomSequence s WITH(HOLDLOCK)
    WHERE   s.Name = @CustomSequenceName
    AND     s.LastYear = @Year
COMMIT

来源：https://stackoverflow.com/questions/45469183/how-to-change-the-series-of-zeroes-in-a-computed-column

标签

sql-server

database

calculated-columns

computed-field