Question

I have a query which produces flattened hierarchy from a parent-child table (self join, adjacent list). The problem is that this query produces NULLs for levels which does not have any child. Now my intention is to ‘backfill’ these levels to produce a table which does not contain any NULL values in level columns. How should I modify this query?

Example data:

SET NOCOUNT ON;
USE Tempdb;

IF OBJECT_ID('dbo.Employees', 'U') IS NOT NULL DROP TABLE dbo.Employees;

CREATE TABLE dbo.Employees
(
  empid   INT         NOT NULL PRIMARY KEY,
  mgrid   INT         NULL     REFERENCES dbo.Employees,
  empname VARCHAR(25) NOT NULL,
  salary  MONEY       NOT NULL,
  CHECK (empid <> mgrid),
  CHECK (empid > 0)
);

CREATE UNIQUE INDEX idx_unc_mgrid_empid ON dbo.Employees(mgrid, empid);

INSERT INTO dbo.Employees(empid, mgrid, empname, salary) VALUES
  (1,  NULL, 'David'  , $10000.00),
  (2,  1,    'Eitan'  ,  $7000.00),
  (3,  1,    'Ina'    ,  $7500.00),
  (4,  2,    'Seraph' ,  $5000.00),
  (5,  2,    'Jiru'   ,  $5500.00),
  (6,  2,    'Steve'  ,  $4500.00),
  (7,  3,    'Aaron'  ,  $5000.00),
  (8,  5,    'Lilach' ,  $3500.00),
  (9,  7,    'Rita'   ,  $3000.00),
  (10, 5,    'Sean'   ,  $3000.00),
  (11, 7,    'Gabriel',  $3000.00),
  (12, 9,    'Emilia' ,  $2000.00),
  (13, 9,    'Michael',  $2000.00),
  (14, 9,    'Didi'   ,  $1500.00);

query provided by @Andomar

; with  Tree as
        (
        SELECT  empid
        ,       mgrid
        ,       1 as lv
        ,       1 as level1
        ,       null as level2
        ,       null as level3
        ,       null as level4
        ,       null as level5
        FROM    Employees
        WHERE   mgrid IS NULL 
        UNION ALL
        SELECT  E.empid
        ,       E.mgrid
        ,       T.lv + 1
        ,       T.level1
        ,       case when T.lv = 1 then E.empid else t.level2 end
        ,       case when T.lv = 2 then E.empid else t.level3 end
        ,       case when T.lv = 3 then E.empid else t.level4 end
        ,       case when T.lv = 4 then E.empid else t.level5 end
        FROM    Employees AS E
        JOIN    Tree T
        ON      E.mgrid = T.empid
        )
select  *
from    Tree
order by empid

This yields

+-------+--------+----+--------+--------+--------+--------+--------+
| EMPID | MGRID  | LV | LEVEL1 | LEVEL2 | LEVEL3 | LEVEL4 | LEVEL5 |
+-------+--------+----+--------+--------+--------+--------+--------+
|     1 | (null) |  1 |      1 | (null) | (null) | (null) | (null) |
|     2 | 1      |  2 |      1 | 2      | (null) | (null) | (null) |
|     3 | 1      |  2 |      1 | 3      | (null) | (null) | (null) |
|     4 | 2      |  3 |      1 | 2      | 4      | (null) | (null) |
|     5 | 2      |  3 |      1 | 2      | 5      | (null) | (null) |
|     6 | 2      |  3 |      1 | 2      | 6      | (null) | (null) |
|     7 | 3      |  3 |      1 | 3      | 7      | (null) | (null) |
|     8 | 5      |  4 |      1 | 2      | 5      | 8      | (null) |
|     9 | 7      |  4 |      1 | 3      | 7      | 9      | (null) |
|    10 | 5      |  4 |      1 | 2      | 5      | 10     | (null) |
|    11 | 7      |  4 |      1 | 3      | 7      | 11     | (null) |
|    12 | 9      |  5 |      1 | 3      | 7      | 9      | 12     |
|    13 | 9      |  5 |      1 | 3      | 7      | 9      | 13     |
|    14 | 9      |  5 |      1 | 3      | 7      | 9      | 14     |
+-------+--------+----+--------+--------+--------+--------+--------+

but the idea is to achieve this

+-------+--------+----+--------+--------+--------+--------+--------+
| EMPID | MGRID  | LV | LEVEL1 | LEVEL2 | LEVEL3 | LEVEL4 | LEVEL5 |
+-------+--------+----+--------+--------+--------+--------+--------+
|     1 | (null) |  1 |      1 | 1      | 1      | 1      | 1      |
|     2 | 1      |  2 |      1 | 2      | 2      | 2      | 2      |
|     3 | 1      |  2 |      1 | 3      | 3      | 3      | 3      |
|     4 | 2      |  3 |      1 | 2      | 4      | 4      | 4      |
|     5 | 2      |  3 |      1 | 2      | 5      | 5      | 5      |
|     6 | 2      |  3 |      1 | 2      | 6      | 6      | 6      |
|     7 | 3      |  3 |      1 | 3      | 7      | 7      | 7      |
|     8 | 5      |  4 |      1 | 2      | 5      | 8      | 8      |
|     9 | 7      |  4 |      1 | 3      | 7      | 9      | 9      |
|    10 | 5      |  4 |      1 | 2      | 5      | 10     | 10     |
|    11 | 7      |  4 |      1 | 3      | 7      | 11     | 11     |
|    12 | 9      |  5 |      1 | 3      | 7      | 9      | 12     |
|    13 | 9      |  5 |      1 | 3      | 7      | 9      | 13     |
|    14 | 9      |  5 |      1 | 3      | 7      | 9      | 14     |
+-------+--------+----+--------+--------+--------+--------+--------+

Answer 1

Just Add the below after the Tree CTE

Select empid,mgrid,lv,
        level1 = coalesce(level1,Rn),
        level2 = coalesce(level2,Rn),
        level3 = coalesce(level3,Rn),
        level4 = coalesce(level4,Rn),
        level5 = coalesce(level5,Rn)
from
(select  empid,mgrid,lv,level1,level2,level3,level4,level5,Row_Number()Over(Order By empid) as Rn
from    Tree)x