SQL SERVER：每7行自动增加7

Question

I am trying to normalize a WeekOfYear column and my current format of the table looks somewhat like this:

Week  DOW
  1  FRIDAY
     SATURDAY
     SUNDAY
     MONDAY
     TUESDAY
     ...
  2  FRIDAY
     SATURDAY
     SUNDAY
     MONDAY
     TUESDAY
     ...

How can I essentially pad in the missing values in the 'Week' column so it looks like this:

Week  DOW
  1  FRIDAY
  1  SATURDAY
  1  SUNDAY
  1   MONDAY
  1  TUESDAY
  1  ...
  2  FRIDAY
  2  SATURDAY
  2  SUNDAY
  2  MONDAY
  2  TUESDAY
  2  ...

Here is a SQL query that creates a simple version of my problem's sample data:

CREATE TABLE dbo.foobar
(
 Wk CHAR(2),
 DOW CHAR(10)
 );


 INSERT INTO dbo.foobar(Wk, DOW)
 VALUES 
 (1, 'FRIDAY'),
 (NULL,'SATURDAY'),
 (NULL,'SUNDAY'),
 (2, 'FRIDAY'),
 (NULL,'SATURDAY'),
 (NULL,'SUNDAY')


 SELECT * FROM dbo.foobar

My initial thoughts are to use some kind of built in auto-increment function, but if that does not exist then I would write some CASE statement that would say if the current row is blank, then use the number from the preceding row.

Any thoughts would be greatly appreciated.

Thanks in advance!

Answer 1

SQL tables are inherently unordered. So, with the sample data you provide, you cannot do what you want.

If you add a primary key to specify the ordering, then you can do what you want. This would look like:

CREATE TABLE dbo.foobar (
    pk int not null identity(1, 1) primary key,
    Wk CHAR(2),
    DOW CHAR(10)
 );


INSERT INTO dbo.foobar(Wk, DOW)
  VALUES (1, 'FRIDAY'),
         (NULL,'SATURDAY'),
         (NULL,'SUNDAY'),
         (2, 'FRIDAY'),
         (NULL,'SATURDAY'),
         (NULL,'SUNDAY');

 SELECT * FROM dbo.foobar;

The rest of this assumes that the primary key is appropriately ordered but not necessarily gap-free.

You can then do what you want with simple arithmetic:

select 1 + (row_number() over (order by pk) - 1) / 7 as newwk, f.*
from foobar;

Alternatively, if you wanted to keep the current value, you can use the arithmetic to define groups and then "spread" the value in the group:

select max(wk) over (partition by grp) as newwk, f.*
from (select 1 + (row_number() over (order by pk) - 1) / 7 as grp, f.*
      from foobar f
     ) f;

EDIT:

The above assumes that you have 7 items per group. If this is not true, you can just count the valid value of wk :

select max(wk) over (partition by grp) as newwk, f.*
from (select (count(wk) over (order by pk)) as grp, f.*
      from foobar f
     ) f;

Here is a SQL Fiddle.

Answer 2

I assume you have some identity pk in your table to guarantee ordering:

select wk as oldwk, 
       dow, 
       (select top 1 wk 
        from foobar f2 
        where f2.id <= f1.id and f2.wk is not null
        order by f2.id desc) as newwk
from foobar f1

For update:

update f1
set wk = (select top 1 wk 
          from foobar f2 
          where f2.id <= f1.id and f2.wk is not null
          order by f2.id desc)
from foobar f1