SQL Update only updates one row - sql

Question

This code is only updating one row, why? It has to do with one of the sub-queries but I am not sure. I'm thinking the WHERE..IN in the UPDATE statement but I am not sure.
UPDATE [sde].[sy1].[Valve_evw]
SET [sde].[sy1].[Valve_evw].[MA]
= (SELECT [sde].[sy1].[Valve_Join_evw].[MC]
FROM [sde].[sy1].[Valve_Join_evw])
WHERE [sde].[sy1].[Valve_evw].[PrimaryKey]
IN (SELECT [sde].[sy1].[Valve_Join_evw].[PrimaryKey]
FROM [sde].[sy1].[Valve_Join_evw]
WHERE [sde].[sy1].[Valve_Join_evw].[MA]
!= [sde].[sy1].[Valve_Join_evw].[MC])
Context:
What I am trying to do is update the MA column in Valve_evw using the MC column in Valve_Join_evw. The PrimaryKey in Valve_evw references equivalent rows as the PrimaryKey in Valve_Join_evw. As in, a single row in Valve_Join_evw will have the same PrimaryKey as a single row in Valve_evw, thus that equivalency can be used to update the records in Valve_evw. Also the MA column is equivalent in both tables. [Note: The Valve_Join_evw table is created with ESRI mapping software using the spatial relationship between the Valve_evw and a separate table, this is how the duplicate rows exist]
I am using database views (hence the '_evw') in SQL Server with a default INSTEAD OF UPDATE trigger. This combination, views and trigger, prevents the use of table joins to do this update. I have also tried MERGE but that will not work either. Therefore I am stuck with the ANSI standard, hence the sub-queries. This script runs with no errors but it only updates a single row whereas there are about 9000 thousand rows in the tables.
The output message:
(1 row(s) affected)
(0 row(s) affected)

Answer 1

First of all let's reduce the eye hurting SQL to what it really is:
update sde.sy1.valve_evw
set ma = (select mc from sde.sy1.valve_join_evw)
where primarykey in (select primarykey from sde.sy1.valve_join_evw where ma <> mc)
WHERE clause
We look for all primarykey in valve_join_evw where a record's ma <> mc. We update all valve_evw records with such primarykey.
SET clause
For a record we want to update, we set ma to the value found with:
select mc from sde.sy1.valve_join_evw
But this query has no where clause, so what value does it select to fill the record's ma field? It selects all mc from valve_join_evw, so the DBMS probably picks one of these values arbitrarily. (It would be better, it raised an error.)
Conclusion
It is very easy to see which records the statement will update.
Which primarykey:
select primarykey from sde.sy1.valve_join_evw where ma <> mc
Which rows:
select *
from sde.sy1.valve_evw
where primarykey in (select primarykey from sde.sy1.valve_join_evw where ma <> mc)
As to the SET clause: Add a WHERE clause to your subquery that relates the record to select to the record to update (same ma? same primarykey?) E.g.:
set ma =
(
select mc
from sde.sy1.valve_join_evw vj
where vj.primarykey = valve_evw.primarykey
and vj.ma = valve_evw.ma
)

Answer 2

Hi there i recomend first to do the select statement and when you are ok with te records retrieved use the same where for the update statement

Answer 3

Here is what the final script looks like.
UPDATE [Valve_evw]
SET [Valve_evw].[MA] =
(
SELECT [Valve_Join_evw].[MC]
FROM [Valve_Join_evw]
WHERE[Valve_Join_evw].[PrimaryKey] = [Valve_evw].[PrimaryKey]
)
WHERE [Valve_evw].[PrimaryKey]
IN (
SELECT [Valve_Join_evw].[PrimaryKey]
FROM [Valve_Join_evw]
WHERE [Valve_Join_evw].[MA]
!= [Valve_Join_evw].[MC]
);