How to write a sql query to calculate weights using CTE

Question

Hi guys,
want some help using a CTE to generate data using recursive SQL - input data in table A to be transformed into table B shown below
Table A
Instru_id_index     instru_id_name    instru_id_constit  con_name   weight
        56                       INDEX A                     
23                  A                 25
        56                       INDEX A                     
24                 B                  25
        56                       INDEX A                     
25                  C                 25
        56                       INDEX A                     
57              
INDEX  B       25
        57                      
INDEX B                     31                 
D                 33
        57                      
INDEX B                     32                 
E                  33
        57                      
INDEX B                     33                 
F                  33
(Logic should be recursive in order to be able to handle multi-level, not just level 2.)
Table B
Instru_id_index     instru_id_name    instru_id_constit  constit_name   weight
        56                       INDEX A                        
23                A                   25
        56                       INDEX A                        
24                B                   25
        56                       INDEX A                        
25                C                   25
        56                       INDEX A                        
31                D                   8.3
        56                       INDEX A                        
32                E                    8.3
        56                       INDEX A                        
33                F                    8.3
        57                       
INDEX B                       31                
D                   33
        57                       
INDEX B                       32                E                   
33
        57                       
INDEX B                       33               
F                     33
how can I write a simple CTE construct to  display the data in table B -  How can i calculate the values of weights as 8.3 respectively - calculate these without changing the structure of the tables.
Can I do this in a CTE

Answer 1

Full join?
Anyway, thanks for Rsignh to produces a script with CREATE TABLE and INSERT statements. I've extended the data to one more level of recursion.
create table weight_tab(
 instrument_id_index int,
 instrument_id_name varchar(10),
 instrument_id_constituent int,
 constituent_name varchar(10),
 [weight] decimal(10,2))
 insert into weight_tab values
 (56,'INDEX A',23,'A',25),(56,'INDEX A', 24,'B',25),
(56,'INDEX A',25,'C',25),(56,'INDEX A', 57,'INDEX  B',25),
(57,'INDEX B',31,'D',33), (57,'INDEX B', 32,'INDEX E',33),
(57,'INDEX B',33,'INDEX C',33),
(33,'INDEX C',42,'Alfa',60),
(33,'INDEX C',43,'Beta',40),
(32,'INDEX C',142,'Gamma',90),
(32,'INDEX C',143,'Delta',10)
go
SELECT * FROM weight_tab
go
; WITH rekurs AS (
    SELECT instrument_id_index, instrument_id_name, instrument_id_constituent,
           cast(weight as float) AS weight, cnt = 1
    FROM   weight_tab a
    WHERE  NOT EXISTS (SELECT *
                       FROM   weight_tab b
                       WHERE  b.instrument_id_constituent = a.instrument_id_index)
    UNION ALL
    SELECT r.instrument_id_index, r.instrument_id_name, w.instrument_id_constituent,
           r.weight * w.weight / 100, r.cnt  + 1
    FROM   rekurs r
    JOIN   weight_tab w ON r.instrument_id_constituent = w.instrument_id_index
    WHERE r.cnt < 4
SELECT instrument_id_index, instrument_id_name, instrument_id_constituent,
       cast(weight AS decimal(10,2))
FROM   rekurs
go
DROP TABLE weight_tab
Erland Sommarskog, SQL Server MVP, [email protected]