SQL INNER QUERY returns more than one value in an UPDATE query

Question

I have a table to be updated using records of another table and I am doing this to bring over information from one system (database) to another. The scenario is bit complex, but I desperately need help :-s

There are 3 tables - component , scan and stage_link

component

component_id  stage_id
------------  --------
1              NULL
2              NULL
3              NULL
4              NULL
5              NULL

scan

scan_id  component_id  scanner_id           date_scanned
-------  ------------  ----------  -----------------------
 1         1           scanner_a    2012-01-01 07:25:15.125
 2         1           scanner_b    2012-01-02 08:14:05.456
 3         2           scanner_a    2012-01-01 12:05:45.465
 4         3           scanner_a    2012-01-01 19:45:12.536
 5         1           scanner_c    2012-01-03 23:33:54.243
 6         2           scanner_b    2012-01-02 11:59:12.545

stage_link

stage_link_id  scanner_id  stage_id
    -------     ----------  ----------  
       1         scanner_a    1   
       2         scanner_b    1    
       3         scanner_c    2    
       4         scanner_d    2    
       5         scanner_e    2   
       6         scanner_f    3  

I need to update the table component and set the field stage_id according to the latest scan. Each scan takes the component to a stage according to the scanner involved. I have written the following query in order to update the table component, but it throws an error saying;

Subquery returned more than 1 value. This is not permitted when the subquery follows '='

The query is;

UPDATE component
SET stage_id = (select stage_id
                from(
                    select scn.scanner_id, sl.stage_id
                    from scan scn
                    INNER JOIN stage_link sl ON scn.scanner_id = sl.scanner_id
                    where scn.date_scanned = (  select temp_a.max_date 
                                                from (  SELECT x.component_id, MAX(x.date_scanned) as max_date
                                                        FROM scan x
                                                        where component_id = x.component_id 
                                                        GROUP BY x.component_id
                                                      ) as temp_a
                                                where component_id = temp_a.component_id)
                    ) as temp_b
                )

I am working on MS SQL Server and want to sort this out using no PHP or any other language.

I have tried for a day to make this work but still didn't get a way to make this work. Any help would be highly appreciated!

Thank you very much in advance :-)

Answer 1

Check this out without using correlated subqueries:

UPDATE  Com
SET     stage_id = Temp4.stage_id
FROM    dbo.component Com
        INNER JOIN 
        ( 
            SELECT Temp2.component_id ,SL.stage_id
            FROM   dbo.stage_link SL
            INNER JOIN (
                            SELECT component_id ,scanner_id
                            FROM   scan
                            WHERE  date_scanned IN (
                                SELECT  MaxScanDate
                                FROM    
                                ( 
                                    SELECT component_id , MAX(date_scanned) MaxScanDate
                                    FROM scan
                                    GROUP BY component_id
                                ) Temp 
                            )
                        ) Temp2 ON Temp2.scanner_id = SL.scanner_id
        ) Temp4 ON Com.component_id = Temp4.component_id

The output:

component_id stage_id
------------ -----------
1            2
2            1
3            1
4            NULL
5            NULL