重置序列

Question

我已经阅读了几篇关于TSQL身份错误的帖子,并且一直在使用SEQUENCE.但是,我很想知道重置表中SEQUENCE的ID值.举个例子:

CREATE SEQUENCE Inc
    AS INT
    START WITH 1
    INCREMENT BY 1
    CYCLE 
    CACHE 

-- Quick ability to redo everything if needed:
-- DROP SEQUENCE Inc

-- Our table grabs the next sequence for our ID field:
CREATE TABLE SequenceID(
    NewIDField INT DEFAULT NEXT VALUE FOR Inc,
    Name VARCHAR(100)
)

INSERT INTO SequenceID (Name)
VALUES ('John')
    , ('Tiffany')
    , ('Bob')
    , ('Jessica')

SELECT *
FROM SequenceID

-- We remove Bob:
DELETE FROM SequenceID
WHERE NewIDField = 3

-- ID value 3 is gone; it moves from 1 to 2 to 4
SELECT *
FROM SequenceID

INSERT INTO SequenceID (Name)
VALUES ('David')
    , ('Rosa')
    , ('Samuel')

-- ID 3 doesn't exist because the SEQUENCE grabs the next value from 4
SELECT *
FROM SequenceID

-- Let's just reset our ID
;WITH ResetIt AS(
    SELECT ROW_NUMBER() OVER (ORDER BY NewIDField) AS ID
        , NewIDField AS ExistingID
        , Name
    FROM SequenceID
)
UPDATE SequenceID
SET NewIDField = ResetIt.ID
FROM ResetIt
WHERE SequenceID.NewIDField = ResetIt.ExistingID

-- Yay!
SELECT *
FROM SequenceID

INSERT INTO SequenceID (Name)
VALUES ('Sarah')

-- Oh Sarah, tsk tsk.
SELECT *
FROM SequenceID

DROP TABLE SequenceID

有没有办法用SEQUENCE自动执行此操作,我们可以确定最后一个值并从那里开始(类似于RESEED),即使IDENTITY我们删除一个值,我们仍然必须RESEED看到:

CREATE TABLE IDID(
    ID INT IDENTITY(1,1),
    I INT
)

INSERT INTO IDID (I)
VALUES (1),(2),(3),(4)

SELECT *
FROM IDID

DELETE FROM IDID
WHERE ID = 3

INSERT INTO IDID (I)
VALUES (5),(6),(7)

SELECT *
FROM IDID

DROP TABLE IDID

Answer 1

执行更新后,您必须运行一些动态SQL,因为ALTER SEQUENCE只接受RESTART WITH子句的常量:

DECLARE @resetSQL nvarchar(255) = 'ALTER SEQUENCE Inc RESTART WITH ' + (SELECT CAST(MAX(NewIDField)+1 as nvarchar(10)) FROM SequenceID);

exec sp_executesql @resetSQL;