How to load grouped data with SSIS - sql

Question

I have a tricky flat file data source. The data is grouped, like this:
Country City
U.S. New York
Washington
Baltimore
Canada Toronto
Vancouver
But I want it to be this format when it's loaded in to the database:
Country City
U.S. New York
U.S. Washington
U.S. Baltimore
Canada Toronto
Canada Vancouver
Anyone has met such a problem before? Got a idea to deal with it?
The only idea I got now is to use the cursor, but the it is just too slow.
Thank you!

Answer 1

The answer by cha will work, but here is another in case you need to do it in SSIS without temporary/staging tables:
You can run your dataflow through a Script Transformation that uses a DataFlow-level variable. As each row comes in the script checks the value of the Country column.
If it has a non-blank value, then populate the variable with that value, and pass it along in the dataflow.
If Country has a blank value, then overwrite it with the value of the variable, which will be last non-blank Country value you got.
EDIT: I looked up your error message and learned something new about Script Components (the Data Flow tool, as opposed to Script Tasks, the Control Flow tool):
The collection of ReadWriteVariables is only available in the
PostExecute method to maximize performance and minimize the risk of
locking conflicts. Therefore you cannot directly increment the value
of a package variable as you process each row of data. Increment the
value of a local variable instead, and set the value of the package
variable to the value of the local variable in the PostExecute method
after all data has been processed. You can also use the
VariableDispenser property to work around this limitation, as
described later in this topic. However, writing directly to a package
variable as each row is processed will negatively impact performance
and increase the risk of locking conflicts.
That comes from this MSDN article, which also has more information about the Variable Dispenser work-around, if you want to go that route, but apparently I mislead you above when I said you can set the value of the package variable in the script. You have to use a variable that is local to the script, and then change it in the Post-Execute event handler. I can't tell from the article whether that means that you will not be able to read the variable in the script, and if that's the case, then the Variable Dispenser would be the only option. Or I suppose you could create another variable that the script will have read-only access to, and set its value to an expression so that it always has the value of the read-write variable. That might work.

Answer 2

Yes, it is possible. First you need to load the data to a table with an IDENTITY column:
-- drop table #t
CREATE TABLE #t (id INTEGER IDENTITY PRIMARY KEY,
Country VARCHAR(20),
City VARCHAR(20))
INSERT INTO #t(Country, City)
SELECT a.Country, a.City
FROM OPENROWSET( BULK 'c:\import.txt',
FORMATFILE = 'c:\format.fmt',
FIRSTROW = 2) AS a;
select * from #t
The result will be:
id Country City
----------- -------------------- --------------------
1 U.S. New York
2 Washington
3 Baltimore
4 Canada Toronto
5 Vancouver
And now with a bit of recursive CTE magic you can populate the missing details:
;WITH a as(
SELECT Country
,City
,ID
FROM #t WHERE ID = 1
UNION ALL
SELECT COALESCE(NULLIF(LTrim(#t.Country), ''),a.Country)
,#t.City
,#t.ID
FROM a INNER JOIN #t ON a.ID+1 = #t.ID
)
SELECT * FROM a
OPTION (MAXRECURSION 0)
Result:
Country City ID
-------------------- -------------------- -----------
U.S. New York 1
U.S. Washington 2
U.S. Baltimore 3
Canada Toronto 4
Canada Vancouver 5
Update:
As Tab Alleman suggested below the same result can be achieved without the recursive query:
SELECT ID
, COALESCE(NULLIF(LTrim(a.Country), ''), (SELECT TOP 1 Country FROM #t t WHERE t.ID < a.ID AND LTrim(t.Country) <> '' ORDER BY t.ID DESC))
, City
FROM #t a
BTW, the format file for your input data is this (if you want to try the scripts save the input data as c:\import.txt and the format file below as c:\format.fmt):
9.0
2
1 SQLCHAR 0 11 "" 1 Country SQL_Latin1_General_CP1_CI_AS
2 SQLCHAR 0 100 "\r\n" 2 City SQL_Latin1_General_CP1_CI_AS