sql server - sql update (help me )

Question

I have 3 tables:

tbl_indicator

grp_nbr,   sect_nbr,   indicat  
1             100          p  
2             101          s

tbl_group 

grp_id,    grp_nbr,    sect_nbr,     indicat  
333         1              100           a  
555         1              100           p  
444         2              101           s
222         2              101           y

Here (in tbl_group) grp_id is Primary Key

tbl_order

order_id,       grp_id
5000              333
5001              555
5002              555
5003              555
5004              444
5005              444
5006              222

Here (in tbl_order) grp_id is a Foreign Key to grp_id in tbl_group.

In table tbl_indiactor, for one set of grp_nbr and sect_nbr there is an indicat, for the same set of grp_nbr and sect_nbr there is a correct indicat(555,1, 100, p) and a junk indicat(333, 1, 100, a) in table tbl_group, but both these grp_id s(333, 555) are present in table tbl_orders.

Now i need to update tbl_order table in such a way that the junk grp_id s should be replaced with correct grp_id s

The output should like:

tbl_orders

order_id,       grp_id
5000              555
5001              555
5002              555
5003              555
5004              444
5005              444
5006              444

here is a small change

tbl_indicator

grp_nbr, sect_nbr, indicat
01 100 p
02 101 s tbl_group

grp_id, grp_nbr, sect_nbr, indicat
333 01 100 a
555 01 100 p
444 02 101 s 222 2 101 y Here (in tbl_group) grp_id is Primary Key

the junk data(indicat) in group table (222, 22, 101, y) the grp_nbr has one character length but the grp_nbr in tbl_indicat has two character length... how can we handle this??

Answer 1

First, figure out which records need to be updated:

select *
from tbl_order o
inner join tbl_group g on
    g.grp_id = o.grp_id
inner join tbl_indicator i on
    i.grp_nbr = g.grp_nbr
    and i.sect_nbr = g.sect_nbr
where
    g.indicat != i.indicat

Now, modify the query to update those records with the correct grp_id. Notice that I've added an extra join to the tbl_group table with an alias of "g2". This will be the correct group.

update o set
    o.grp_id = g2.grp_id
from tbl_order o
inner join tbl_group g on
    g.grp_id = o.grp_id
inner join tbl_indicator i on
    i.grp_nbr = g.grp_nbr
    and i.sect_nbr = g.sect_nbr
inner join tbl_group g2 on
    g2.grp_nbr = i.grp_nbr
    and g2.sect_nbr = i.sect_nbr
    and g2.indicat = i.indicat
where
    g.indicat != i.indicat

Note that due to the inner join on tbl_group g2, the records will not be updated if there does not exist any tbl_group record where indicat matches the indicat value of its associated tbl_indicator record.