Set-based approach to updating multiple tables, rather than a WHILE loop? - sql-server

Question

Apparently I'm far too used to procedural programming, and I don't know how to handle this with a set-based approach.
I have several temporary tables in SQL Server, each with thousands of records. Some of them have tens of thousands of records each, but they're all part of a record set. I'm basically loading a bunch of xml data that looks like this:
<root>
<entry>
<id-number>12345678</id-number>
<col1>blah</col1>
<col2>heh</col2>
<more-information>
<col1>werr</col1>
<col2>pop</col2>
<col3>test</col3>
</more-information>
<even-more-information>
<col1>czxn</col1>
<col2>asd</col2>
<col3>yyuy</col3>
<col4>moat</col4>
</even-more-information>
<even-more-information>
<col1>uioi</col1>
<col2>qwe</col2>
<col3>rtyu</col3>
<col4>poiu</col4>
</even-more-information>
</entry>
<entry>
<id-number>12345679</id-number>
<col1>bleh</col1>
<col2>sup</col2>
<more-information>
<col1>rrew</col1>
<col2>top</col2>
<col3>nest</col3>
</more-information>
<more-information>
<col1>234k</col1>
<col2>fftw</col2>
<col3>west</col3>
</more-information>
<even-more-information>
<col1>asdj</col1>
<col2>dsa</col2>
<col3>mnbb</col3>
<col4>boat</col4>
</even-more-information>
</entry>
</root>
Here's a brief display of what the temporary tables look like:
Temporary Table 1 (entry):
+------------+--------+--------+
| UniqueID | col1 | col2 |
+------------+--------+--------+
| 732013 | blah | heh |
| 732014 | bleh | sup |
+------------+--------+--------+
Temporary Table 2 (more-information):
+------------+--------+--------+--------+
| UniqueID | col1 | col2 | col3 |
+------------+--------+--------+--------+
| 732013 | werr | pop | test |
| 732014 | rrew | top | nest |
| 732014 | 234k | ffw | west |
+------------+--------+--------+--------+
Temporary Table 3 (even-more-information):
+------------+--------+--------+--------+--------+
| UniqueID | col1 | col2 | col3 | col4 |
+------------+--------+--------+--------+--------+
| 732013 | czxn | asd | yyuy | moat |
| 732013 | uioi | qwe | rtyu | poiu |
| 732014 | asdj | dsa | mnbb | boat |
+------------+--------+--------+--------+--------+
I am loading this data from an XML file, and have found that this is the only way I can tell which information belongs to which record, so every single temporary table has the following inserted at the top:
T.value('../../id-number[1]', 'VARCHAR(8)') UniqueID,
As you can see, each temporary table has a UniqueID assigned to it's particular record to indicate that it belongs to the main record. I have a large set of items in the database, and I want to update every single column in each non-temporary table using a set-based approach, but it must be restricted by UniqueID.
In tables other than the first one, there is a Foreign_ID based on the PrimaryKey_ID of the main table, and the UniqueID will not be inserted... it's just to help tell what goes where.
Here's the exact logic that I'm trying to figure out:
If id-number currently exists in the main table, update tables based on the PrimaryKey_ID number of the main table, which is the same exact number in every table's Foreign_ID. The foreign-key'd tables will have a totally different number than the id-number -- they are not the same.
If id-number does not exist, insert the record. I have done this part.
However, I'm currently stuck in the mind-set that I have to set temporary variables, such as #IDNumber, and #ForeignID, and then loop through it. Not only am I getting multiple results instead of the current result, but everyone says WHILE shouldn't be used, especially for such a large volume of data.
How do I update these tables using a set-based approach?

Answer 1

Assuming you already have this XML extracted, you could do something similar to:
UPDATE ent
SET ent.col1 = tmp1.col1,
ent.col2 = tmp1.col2
FROM dbo.[Entry] ent
INNER JOIN #TempEntry tmp1
ON tmp1.UniqueID = ent.UniqueID;
UPDATE mi
SET mi.col1 = tmp2.col1,
mi.col2 = tmp2.col2,
mi.col3 = tmp2.col3
FROM dbo.[MoreInformation] mi
INNER JOIN dbo.[Entry] ent -- mapping of Foreign_ID ->UniqueID
ON ent.PrimaryKey_ID = mi.Foreign_ID
INNER JOIN #TempMoreInfo tmp2
ON tmp2.UniqueID = ent.UniqueID
AND tmp2.SomeOtherField = mi.SomeOtherField; -- need 1 more field
UPDATE emi
SET ent.col1 = tmp3.col1,
emi.col2 = tmp3.col2,
emi.col3 = tmp3.col3,
emi.col4 = tmp3.col4
FROM dbo.[EvenMoreInformation] emi
INNER JOIN dbo.[Entry] ent -- mapping of Foreign_ID ->UniqueID
ON ent.PrimaryKey_ID = mi.Foreign_ID
INNER JOIN #TempEvenMoreInfo tmp3
ON tmp3.UniqueID = ent.UniqueID
AND tmp3.SomeOtherField = emi.SomeOtherField; -- need 1 more field
Now, I should point out that if the goal is truly to
update every single column in each non-temporary table
then there is a conceptual issue for any sub-tables that have multiple records. If there is no record in that table that will remain the same outside of the Foreign_ID field (and I guess the PK of that table?), then how do you know which row is which for the update? Sure, you can find the correct Foreign_ID based on the UniqueID mapping already in the non-temporary Entry table, but there needs to be at least one field that is not an IDENTITY (or UNIQUEIDENTIFIER populated via NEWID or NEWSEQUENTIALID) that will be used to find the exact row.
If it is not possible to find a stable, matching field, then you have no choice but to do a wipe-and-replace method instead.
P.S. I used to recommend the MERGE command but have since stopped due to learning of all of the bugs and issues with it. The "nicer" syntax is just not worth the potential problems. For more info, please see Use Caution with SQL Server's MERGE Statement.

Answer 2

you can use MERGE which does upsert ( update and insert ) in a single statement
First merge entries to the main table
For other tables, you can do a join with main table to get foreign id mapping
MERGE Table2 as Dest
USING ( select t2.*, m.primaryKey-Id as foreign_ID
from #tempTable2 t2
join mainTable m
on t2.id-number = m.id-number
) as Source
on Dest.Foreign_ID = m.foreign_ID
WHEN MATCHED
THEN Update SET Dest.COL1 = Source.Col1
WHEN NOT MATCHED then
INSERT (FOREGIN_ID, col1, col2,...)
values ( src.foreign_Id, src.col1, src.col2....)