California accepts Open Source

A policy shift occurred January 7th with the California IT czar.

The CIO has issued a new policy directive that may make it easier for open source platform to compete for the scarce contract dollars available for IT projects.

Oracle and Microsoft dominating the California platform purchase pipeline may still be the norm. My hope is that with this new policy there is some opening of opportunity for good open source offerings and consulting.

Here is the link to the official PDF policy letter:
http://bit.ly/6XTifr

Simple XML query and looping

Working with a client's SQL 2005 stored procedure this week I came across a very complicated series of T-SQL. The jest of the procedure is to loop through a series of rows inside of an XML variable passed into the SP. The implmentation was built using OPENXML and Select statements with patterns. I spoke with the maintainers of the SP and it became clear that the functionality was overly complex and that using XML XQuery and XPath was a new skill set.

So I devised this simple XML sniplet that will run and demonstrates some of the basics available when dealing with XML data. This should click with most first time XML database folks accustomed to working with T-SQL. They can then explore the rich feature set available.

Dave W
--
-- Simple example of using XML query.
-- Build to shold some basics of "looping" through a set of XML "rows"
-- Dave Winters 6 Jan 2010
--
declare @x xml
set @x='
<grills franchise="1" regionname="West">
<location locationid="Sacramento">
<listing>MenuItem Pizza </listing>
<listing>MenuItem Salad </listing>
<listing>MenuItem Sushi </listing>
</location>
<location locationid="Auburn">
<listing>MenuItem french fries </listing>
<listing>MenuItem hamburgres </listing>
<listing>MenuItem coke </listing>
</location>
</grills>'
--
-- Get a specific location menu
--
SELECT @x.query('
for $listItem in /grills/location
where $listItem/@locationid="Auburn"
return $listItem
') as Result
--
-- XML fragments for the location ID attribute, not proper form.
-- To make it regular you'll need to put inside one root element
--
SELECT @x.query('
for $listItem in /grills/location
return <t>{$listItem/@locationid}</t>
')
--
-- Chunking some locations blobs
--
SELECT T.c.query('(.)[1]') as LocXML
FROM @x.nodes('/grills/location') T(c)
--
-- Build the master menu list
--
SELECT T.c.value('(./text())[1]', 'varchar(256)') as Master_Menu_List
FROM @x.nodes('/grills/location/listing') T(c)
--
-- XML is much more prowerful than this simple example.
-- This was to show how you can go through an XML object in a fashion similar to
-- processing records in SQL tables.
--

NULL in SQL databases!!!!!!! What a pain!

I am very passionate about the whole issue surrounding NULL in databases. It is a simple yet exceedingly difficult item.

Let me pass along some ideas and one scenario that I use as guides that has help keep me out of trouble.

1) NULL is NEVER a value! It is the absence of value! Or as EF Codd originally stated: “missing information and inapplicable information”
See: http://en.wikipedia.org/wiki/Null_(SQL)
2) NULL should NEVER EVER be used as a flag in decision logic. Testing for NULL is fine with a narrow constraint that we are checking for NULL state.
3) Setting anything to NULL is not the same as “deleting information.”

Here is a scenario I use to illustrate a simple practical application of these ideas. Assume we have a simple order entry SQL application that has a shipping address form coupled to an address table. Something like:
Create table ShipAddr( CustName varchar(40) null, Street1 varchar(30) null, City varchar(30) null, State varchar(20) null, ZipCode varchar(9) null)

Here is the scenario:

1- Customer orders a product and customer service calls up the shipping address form to fill out the information.
2- The customer supplies all of the information but doesn’t have their Zip code. This field is not updated and the form is saved. The ZipCode field has the original “state” NULL.
3- The next day the customer calls back and supplies the value “35123” as their Zip code. The form is updated and saved. The ZipCode field now has the value “35123”
4- Order fulfillment department runs a check and determines that “35123” is an invalid Zip. The ship address form is updated by deleting all of the values in this field. The form is saved.
IMPORTANT NOTE: Now the ZipCode field has the value “”, or in other words a zero length string!!! Not NULL!

Why not just set it back to NULL? The most important reason is that doing this completely loses the “transitional state” of the field in this record! If you look at classic 3VL and tuple calculus set operations it negates the ability to segregate subsets of the data based on if the value in the field has ever been “touched.” If the field is set back to NULL as a “value” the segregation of records that have never had an address value is lost. How do we also determine that a field in the general sense may actually have a correct value of “”?

Ok at this point you are probably asking yourself … who cares?
Having seen this problem repeated over and over in many SQL implementations I would suggest that this issue is important for several reasons:
1)Maintainability, confusion around NULLs is costly
2) Accuracy, loss of state or ability to validate because of NULL “values” can be expensive
3) Interoperability, NULLs used as values in one table or application may not have the same meaning in another application.

Regards,

Dave W

Finding foreign key references to a table.

At some point you'll find yourself wanting to modify or change the way a table is structured. If your database uses FK (foreign key) constraints it is sometime a pain to find all the FKs referencing the table. Microsoft’s management tool will list dependant objects but drilling down to which tables and columns reference which column on the table you want to modify can take some time.

Here is a little procedure to list out FKs on a target table:
--
-- Find all foreign keys references to a particualr table
-- D Winters
--
declare @targetTab sysname

set @targetTab = 'employee'

select t.name as TableWithForeignKey, object_name(constraint_object_id) as ForeignKeyConstraint,
c.name as ForeignKeyColumn, fk.constraint_column_id as FK_PartNo ,
COL_NAME(referenced_object_id , referenced_column_id ) as References_Column
from sys.foreign_key_columns as fk
inner join sys.tables as t on fk.parent_object_id = t.object_id
inner join sys.columns as c on fk.parent_object_id = c.object_id
and fk.parent_column_id = c.column_id
where fk.referenced_object_id = (select object_id from sys.tables where name = @targetTab)
order by TableWithForeignKey, FK_PartNo