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Tag Archives: sql 2005

Persisting Computed XML

It’s possible to define an XML column as a computed column. And in most cases I think it would make sense to persist the column to save doing all that work again. As Bob Beauchemin points out there’s a trick to doing it.

The first thing you need is a user defined scalar function to [...]

Detecting SQL NULL in XQuery

When using XQuery inside SQL Server the value of SQL variables and columns can be referenced using the sql:column and sql:variable functions respectively. When a SQL value is NULL you may want to mark the XML element as xsi:nil, like the following.

<event_data xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:nil="true" />

The semantic equivalent of SQL NULL in XQuery is an empty [...]

Heap locking under Serializable Transactions

Tables without a clustered index store their data in a Heap data structure. The (in row) data is added to the heap as its encountered without any ordering, rather than ordering by the columns in a clustered index. This makes finding particular rows a little tricky and a lot slower as there is normally no [...]

How long do READ COMMITTED transactions hold shared locks

This was one of the questions I did not answer in my previous look at Shared locks in standard transaction isolations. In that post the lowest level lock the READ COMMITTED test took was an Intent Shared (IS) lock on the single data page in the table. But I do remember reading somewhere that READ [...]

Discovering the Isolation Level

A few times I’ve wondered how to detect the ISOLATION level and have discovered a few.

DBCC USEROPTIONS

DBCC USEROPTIONS

Set Option Value ——————————————————————————- textsize [...]