午夜搬运工

做一个作业，夜深人静的时候搬运数据。如下：

USE [myDB]
GO

DECLARE @i INT;
DECLARE @j INT;
DECLARE @m INT;
DECLARE @offset INT;

SELECT @m = ISNULL(MAX(Id),0) FROM [sourceDB].dbo.[Table];
SET @offset = 1000000;--每处理一百万条提交一次

DECLARE @dayLimit SMALLDATETIME;
SET @dayLimit = DATEADD(hh,5,CONVERT(VARCHAR(10),GETDATE(),120));--时限是凌晨 5点

SET IDENTITY_INSERT [Table] ON;--可显式插入标识列

SELECT @i = ISNULL(MAX(Id),0) + 1 FROM [Table];
SET @j = @i + @offset;
WHILE @i<@m
BEGIN
    IF @j > @m SET @j = @m;

    INSERT INTO [Table]
           (……)
    SELECT ……
    FROM [sourceDB].[dbo].[Table]
    WHERE Id BETWEEN @i AND @j;

    IF DATEDIFF(hh,GETDATE(),@dayLimit) <= 0 RETURN;     --超过时限（凌晨5点）就退出

    SET @i = @j + 1;
    SET @j = @j + @offset;
END

SET IDENTITY_INSERT [Table] OFF;--取消显式插入标识列