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Category: T-SQL

Grouping Data With ROLLUP

Published 2017-11-09 by Kevin Feasel

Steve Jones shows how easy it is to use the ROLLUP function:

I was editing an article recently that talked about ROLLUP, and I wanted to play with this a bit more. I hadn’t used this much in my career, but it’s a handy operator that’s worth including in your toolkit.

ROLLUP is used to provide additional totals for your aggregates while using GROUP BY. Here’s a little example. I’ve got some data for American Football quaterbacks. In this case, I’ve extracted some stats for a few noteworthy players today.

I’ll probably end up using ROLLUP about once every three months and be very pleased when I remember that it exists.  I use GROUPING SETS more often and almost never use CUBE.

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String Splitting With Multi-Character Delimiters

Published 2017-11-01 by Kevin Feasel

Derek Colley shows a way of using the STRING_SPLIT function when your delimiter is more than one character:

But what happens if we try to use STRING_SPLIT with a multi-character separator, like this?

SELECT * FROM STRING_SPLIT(@GodawfulString, ‘,,’)

Msg 214, Level 16, State 11, Line 67
Procedure expects parameter ‘separator’ of type ‘nchar(1)/nvarchar(1)’.

Ah.  That’s a no, then.

Click through for the solution.

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Getting SQL Server Context Settings

Published 2017-11-01 by Kevin Feasel

Frank Gill has a script to find current Query Store context settings:

The following query will return the hex and integer value for each row in the table (NOTE: Query store must be enabled for the database to return values):

USE YourQueryStoreDatabase;

SELECT set_options, CONVERT(INT, set_options) AS IntSetOptions
FROM sys.query_context_settings;

The set_options value represents a bit mask, with each binary digit representing a specific set option. The full list of values can be found here. I created stored procedure ReturnSetOptions to take the IntSetOptions from the query above and return the set options represented. The code for the procedure is listed below.

Read on to get a script which breaks the bitmask field into human-readable results.

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Finding Objects Relating To A Schema

Published 2017-10-30 by Kevin Feasel

Jason Brimhall has a script to help you find which objects are tied to a particular schema:

I have run into this very issue where there are far too many objects in the schema to be able to drop one by one. Add to the problem that I am looking to do this via script. Due to the need to drop the schema and the (albeit self imposed) requirement of doing it via script, I came up with the following that will cover most cases that I have encountered.

Click through for the script.

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Persisting Computed Columns

Published 2017-10-30 by Kevin Feasel

Greg Low describes persisted computed columns:

Each time the value from that column is queried, the calculation is performed so the result can be returned. This makes sense when the value is changing regularly and the value is queried infrequently.

However, according to my completely subjective statistics, most computed columns are queried much more than they are ever changed. So why work the value out each and every time?

One really nice thing about persisted computed columns is that you can then build non-clustered indexes using these columns.  It’s a great way of pre-computing work that you need to do often but which would violate rules of database normalization.

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Line Continuation In T-SQL

Published 2017-10-30 by Kevin Feasel

Solomon Rutzky shows how line continuation works with SQL Server:

While it is not widely used (at least I have never seen anyone besides myself use it), T-SQL does actually have a line-continuation character: \ (backslash). Placing a backslash at the end of a line within a string literal (or constant as the MSDN documentation refers to it) or binary string will ignore the newline after the backslash. For example:

PRINT N'Same
Line';

displays the following in the “Messages” tab:

Same
Line

But, add in the backslash (well, a space and then a backslash so that it looks right):

PRINT N'Same \
Line';

and now the following is displayed in the “Messages” tab:

Same Line

Read on for more details.

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Updating Multiple Tables In One Statement

Published 2017-10-27 by Kevin Feasel

Denis Gobo tries different methods of updating two tables in one statement:

Every now and then you will get someone asking how to update two tables with one statement in SQL Server. The answer is usually, no that is not possible… the person then walks away muttering something about how MySQL allows it.

So I decided to try to see if I could update two tables with one statement. I decided to try a couple of different things

  • view

  • common table expression

  • indexed view

  • instead of trigger

The results are generally negative.  I get the benefit of updating multiple tables in a single query, particularly when you have fairly complex logic around determining which records to update, but if you just wrap things in a transaction, at least you get the benefits of atomicity.  And if you often have to update a bunch of different tables at the same time, there might be an issue with your data model.

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Comparing Ranking Functions

Published 2017-10-20 by Kevin Feasel

Doug Kline compares three window functions:  RANK, DENSE_RANK, and ROW_NUMBER:

— so let’s say that we’ve created a contest

— places in the contest (top place, 2nd place, etc.)
— will be determined by the test score

— in other words, we’re not so concerned with the raw score
— but rather, we’re interested in the *relative* score
— and the order in which people appear, based on their score

— we can use the ROW_NUMBER() function to give a
— ‘ranking’ to each record, based on Score

Doug’s post is a video and an extended script so you can follow along.

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Updating Data In Common Table Expressions

Published 2017-10-20 by Kevin Feasel

Kenneth Fisher shows that you can directly update a table referenced in a common table expression:

CTEs are cool things. You can essentially create one or more in-line view(s) within your query. One thing that isn’t overly well known is that you can actually update the data within the CTE. No, I don’t mean using using the UPDATE statement with a CTE but actually running the update through the CTE.

This is really powerful when combined with window functions, like only updating the first record given a particular partition.  You can also delete, which makes duplicate detection and deletion fairly straightforward.

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Default Schemas In SQL Server

Published 2017-10-13 by Kevin Feasel

Daniel Hutmacher looks at specifying default schemas on a database:

If your user is a database owner, (i.e. is a member of the db_owner group or has CONTROL permissions on the database) the default schema will always be dbo. This is something you can’t change.

So if your legacy application needs quasi-administrative privileges in the database, you can’t make it a database owner, but you can grant those permissions on the schema instead (which is actually a better idea anyway).

What Daniel is doing is akin to the pre-2005 concept of user spaces, where Bob had a schema and Mary had a schema and Jill had a schema and so forth.

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