adventureworks database primary file download 2012

The easiest way to show this is to show both

The definition may state a column as an include that is made into a key column by SQL Server secretly.

I wanted to preserve the definition as the index was created.

I made this design choice for a few reasons: Why doesn’t sp_BlitzIndex® remove “duplicate” secret columns? Then add in the “secret” columns which haven’t already been included.

To determine the columns that will be in an index, look first at the index definition. I repeat, there is no penalty if you list a column from the clustered index in your nonclustered index. It will never have to store a column twice. SQL Server will only ever add columns from the clustering key to an index if you have not specified them in the index. The columns are in the following order: ProductID, WorkOrderID, OperationSequence The effective definition of this nonclustered index is that it has THREE columns in it (not just one, as the creator might have thought). Question: Does that mean the column is stored twice? No, the column is NOT stored twice. It was defined as a key column, but now we’re saying that it’s a secret column as well. You may have noticed that the ProductID column appears twice in sp_BlitzIndex® for this nonclustered index. Those are the exact three columns from our clustered index! (WorkOrderID, ProductID, OperationSequence) Exactly how many columns are in this nonclustered index? There are three secret columns in this nonclustered index, and they have been put in its key: Scrolling over, sp_BlitzIndex® claims that things aren’t so simple. In this case, the secret columns are all in the nonclustered index. The nonclustered index looks very narrow and simple at first. The data is sorted by three key columns: WorkOrderID, ProductID, OperationSequence. Because this is the clustered index we know that it will contain EVERY column in the index all of the data. Primary keys are always unique in SQL Server, so this is a Clustered PK (which is by definition unique). It’s also a Primary Key, indicated by the “”. The definition indicates this with the code “”. This shows us that the table has two indexes. One of these is the clustered index: We can take a look at the indexes, missing indexes, columns, and foreign keys on this table in sp_BlitzIndex® by running the table_name = 'WorkOrderRouting' Let’s take a look at a specific example. The AdventureWorks sample database has a table named Production.WorkOrderRouting. I built sp_BlitzIndex® so that it would give you the information you need about what’s going on in a specific index without having to memorize a whole lot of rules. I never expect anyone to remember this stuff. Please don’t try to memorize that! sp_BlitzIndex® helps make this easier

This made my head spin around the first time I tried to sort it all out. If the clustered index columns are NOT unique, an additional secret column called a “uniquifier” will have already been added to it– and that sneaks into the nonclustered index too.This is done by promoting the clustered key columns to the key of the nonclustered index (otherwise they can be “included” columns).If the nonclustered index is NOT unique, SQL Server makes sure that the columns from the clustering key make it unique behind the scenes.Here’s a quick summary of the rules involved: Exactly how it happens is a little complicated. When this happens, SQL Server will make sure that all of the columns from the clustering key of the table are ALSO in the nonclustered index. In most cases, people create nonclustered indexes on tables that have clustered indexes. (“Secret columns” is a term I made up, because a term didn’t exist yet.) If you don’t add the columns yourself, it goes ahead and does it secretly. In order to accomplish these two tasks, SQL Server always makes sure to add one or more columns to a nonclustered index. It also needs to maintain a relationship between every nonclustered index and its base table. SQL Server needs a unique way to navigate to every row in an index. I wrote sp_BlitzIndex® specifically so that it would rat out some things that SQL Server is doing behind the scenes to secretly help you out– because it’s really better if you know about it.

Adventureworks database primary file download 2012