Cursor in stored procedure

How to Comma separate multiple rows obtained from a SQL Query

Convert multiple rows into one with comma as separator

The basic challenge is to denormalize your resultset so that multiple rows get returned as a single delimited string; while there are several methods for solving this problem, the one that I like (as of SQL 2005) is to use FOR XML PATH, like so:

BEGIN TRAN

ROLLBACK


The multiple results sets are there to illustrate each step in the process; for example, the first output shows what happens when you specify FOR XML PATH with no indicators; SQL Server automatically assigns each row in the resultset to a node named <row>:

<row>,apple</row>
<row>,banana</row>
<row>,tomato</row>

If you specify a tag name in the PATH function, each row will be replaced with that tag name; in the above example, we want an empty tag (‘’).  The result is an XML fragment with no tags:

,apple,banana,tomato

That’s almost what we want, except we need to get rid of the leading comma.  The STUFF command basically replaces the characters in the string supplied (the first parameter; our query FOR XML PATH) starting at a certain position (1 in the example above) and moving forward the specified number of character places (1, the third parameter) with the value of the last parameter (an empty space; the fourth parameter).  The final output is a comma delimited string:

apple,banana,tomato

Straightforward; gotta return to writing.

November and December were a career-changing period for me; things happened that were good, but left me extremely busy at work.  I chose to spend my free time focusing on family time, and I let other things (like my blog and my contributions to the SQL Server community) slide.  Since it’s now a week into January, I thought I would start anew, and try to kick off the year on a good foot.   Instead of making specific resolutions (which I’ll probably break), let me pick a direction and head that way.

First, I want to continue to focus on my family. Last year was an amazing year for me; I got married during the summer, and I had to relearn some things about a healthy family structure.  The first rule is that it takes more than just time; it takes an effort to communicate about things, including those things that are not always easy to say.  If you’ve followed my blog at all, you know that this is my second marriage; my first marriage ended in part because I stopped participating.  Hopefully, I’ve learned from that.

However, I didn’t just bring me into this new union of souls; I have two teenage daughters that I’ve brought along with me.   They need time to get to know their new extended family as well (they now have 10 grandparents, and uncles, aunts, and cousins), and I need to make sure that I keep investing my time in them as well as my wife.   I love these three women very much, and I need to do everything I can to make sure that they know that.   I guess I’m just stating that to lay out the framework for the principles that are following.

Second, I need to focus on my new career.  I got promoted to a management position in mid-November.  I’ve worked for this company for 9 years, and although I’ve been the senior member of the development team for most of that time, this is my first management position ever; I’m now the manager of a newly-formed team of Database Administrators, which means it’s a strange new world for me.  I’ve got to learn to do things a little differently; my goal is not to solve problems, but rather to empower others to solve problems.

Third, I want to be more diligent about my contributions to the community.   This means that I need to lay out specific time for blogging, and other community activities (I’m the treasurer for AtlantaMDF, as well as the organizer for the Eleventy-First SQL Saturday).  I also need to be more focused in my activities; I’ve spent a lot of time recently on StackOverflow, and I probably need to be less obsessive about that; I need scheduled activities, not hit-or-miss.

So there you have it; my simple return to blogging and my New Year’s “resolutions” all wrapped up in a simple package.  I’m still going to have to find time to finish the last series I started, but I’m hoping to find some time in the next few days.  Take me back, just one more time. Please?

VIEWs

According to Books Online, VIEWs create "a virtual table whose contents (columns and rows) are defined by a query. Use this statement to create a view of the data in one or more tables in the database.”  A view encapsulates a SQL SELECT statement to return data, and can be used to provide an alternate representation of data from the original tables.  For example, the following VIEW returns columns from both the Person and Employees tables in the AdventureWorks sample database:


USE AdventureWorks2008R2 ;
GO
IF OBJECT_ID ('hiredate_view', 'V') IS NOT NULL
DROP VIEW hiredate_view ;
GO
CREATE VIEW hiredate_view
AS
SELECT p.FirstName, p.LastName, e.BusinessEntityID, e.HireDate
FROM HumanResources.Employee e
JOIN Person.Person AS p ON e.BusinessEntityID = p.BusinessEntityID ;
GO

Views are not just read-only; in certain cases, VIEWS can be used to insert or update data into underlying tables.  However, discussion of how this works is beyond the intent of this introduction; refer to Books Online fore more information.

Table-Valued Functions (TVF)

Views are not the only virtual structures available in SQL Server; a subset of a user-defined function known as table-valued functions (TVFs) also provide interfaces into the underlying base structures.   Books Online defines table-valued functions as “a Transact-SQL or common language runtime (CLR) routine that accepts parameters, performs an action, such as a complex calculation, and returns the result of that action as… a table.”  There are three types of TVF’s (arranged below in order of increasing complexity): simple, complex, and Common Language Runtime.

Simple TVFs

A simple (or inline) table-valued function is probably the easiest virtual structure to grasp beyond a view; in fact, it’s easily compared to a view with parameters.  A simple TVF encapsulates a SQL statement (much like a view), but it allows for the use of parameters to filter the results returned.  For example, the following simple TVF pulls data from multiple tables for a specific StoreID:

USE AdventureWorks2008R2;
GO
IF OBJECT_ID (N'Sales.ufn_SalesByStore', N'IF') IS NOT NULL
    DROP FUNCTION Sales.ufn_SalesByStore;
GO
CREATE FUNCTION Sales.ufn_SalesByStore (@storeid INT)
RETURNS TABLE
AS
RETURN
(
    SELECT P.ProductID, P.Name, SUM(SD.LineTotal) AS 'Total'
    FROM Production.Product AS P
    JOIN Sales.SalesOrderDetail AS SD ON SD.ProductID = P.ProductID
    JOIN Sales.SalesOrderHeader AS SH ON SH.SalesOrderID = SD.SalesOrderID
    JOIN Sales.Customer AS C ON SH.CustomerID = C.CustomerID
    WHERE C.StoreID = @storeid
    GROUP BY P.ProductID, P.Name
);
GO

Complex TVFs

Complex (or multi-statement) TVF’s are much like their simple counterparts, but allow for greater flexibility in T-SQL coding by adopting a procedural approach to returning tabular data.  A complex TVF requires that a table variable (to be covered later) be defined within the function, and then populated by a series of SQL statements.  The below example from Books Online shows how:

USE AdventureWorks2008R2;
GO
IF OBJECT_ID (N'dbo.ufn_FindReports', N'TF') IS NOT NULL
    DROP FUNCTION dbo.ufn_FindReports;
GO
CREATE FUNCTION dbo.ufn_FindReports (@InEmpID INTEGER)
RETURNS @retFindReports TABLE
(
    EmployeeID INT PRIMARY KEY NOT NULL,
    FirstName NVARCHAR(255) NOT NULL,
    LastName NVARCHAR(255) NOT NULL,
    JobTitle NVARCHAR(50) NOT NULL,
    RecursionLevel INT NOT NULL
)
--Returns a result set that lists all the employees who report to the
--specific employee directly or indirectly.*/
AS
BEGIN
WITH EMP_cte(EmployeeID, OrganizationNode, FirstName, LastName, JobTitle, RecursionLevel) -- CTE name and columns
    AS (
        SELECT e.BusinessEntityID, e.OrganizationNode, p.FirstName, p.LastName, e.JobTitle, 0 -- Get the initial list of Employees for Manager n
        FROM HumanResources.Employee e
           INNER JOIN Person.Person p
           ON p.BusinessEntityID = e.BusinessEntityID
        WHERE e.BusinessEntityID = @InEmpID
        UNION ALL
        SELECT e.BusinessEntityID, e.OrganizationNode, p.FirstName, p.LastName, e.JobTitle, RecursionLevel + 1 -- Join recursive member to anchor
        FROM HumanResources.Employee e
            INNER JOIN EMP_cte
            ON e.OrganizationNode.GetAncestor(1) = EMP_cte.OrganizationNode
           INNER JOIN Person.Person p
           ON p.BusinessEntityID = e.BusinessEntityID
        )
-- copy the required columns to the result of the function
   INSERT @retFindReports
   SELECT EmployeeID, FirstName, LastName, JobTitle, RecursionLevel
   FROM EMP_cte
   RETURN
END;
GO
-- Example invocation
SELECT EmployeeID, FirstName, LastName, JobTitle, RecursionLevel
FROM dbo.ufn_FindReports(1);

Note that code in a multi-statement TVF can involve several steps before returning the final result-set; caution should be used when using complex TVF’s because the optimizer can not determine the cost of these statements during plan estimation.  In short, the more complex the TVF, the more likely that the plan used by SQL Server will be inaccurate.

CLR TVF’s

With the release of SQL Server 2005, Microsoft embedded a limited subset of the functionality from the .NET framework into SQL Server itself, calling it the Common Language Runtime (CLR).  The CLR allows for .NET developers to write and deploy database objects in a managed language (like VB.NET or C#), and allows for very flexible logic for handling data.  A CLR Function is invoked in a fashion similar to other table-valued functions, but the deployment is much more involved (see Books Online for an example using the following steps):

1. Code is written and assembled by a compiler (like Visual Studio).
2. The assembled code must be copied on to the SQL Server.
3. An ASSEMBLY reference is created in T-SQL, which points to the deployed .dll file, and
4. a FUNCTION is created which references the ASSEMBLY.

Next up…

A two-fer: Temporary and Semi-Temporary structures!

1: new to databases, or
2. new to SQL Server

In both cases, we realized that we needed to start having new content in our monthly sessions that was targeted specifically for them, so we decided to start adding a brief 10-minute fundamental session to the beginning of each meeting. I chose to do the first one, and selected a topic called Stuff in the FROM clause. I quickly realized that this could be a nice little blog series, so I’m attempting to expand a 10-minute presentation into a four-part series. Below is the mind map for the presentation:

Stuff in the FROM clause: Base Structures

Base Structures as a category name is a bit misleading, because there’s really only one base structure in any relational database: the table.  Tables are the core of any relational database; they provide storage for data in rows, arranged by columns.  There’s lots of background information on table design, so I won’t spend too much time on it (even that’s too basic for this discussion), but I will highlight some key features about tables:

• From an entity design perspective, a table should represent a set of entities.
• Rows are the un-ordered members of that set
• Columns are the attributes of the entity.
• Table attributes have basic types.
• Tables should have a primary key constraint on one of the columns, which is used to uniquely identify a member of that set.
• Microsoft SQL Server supports a syntax for computed columns, where data for an attribute can be calculated from other attributes.

For Microsoft SQL Server, the CREATE TABLE syntax may be found at: http://msdn.microsoft.com/en-us/library/ms174979.aspx  The simplest table creation statement looks like the following:

CREATE TABLE table_name (column_name column_type)

Next: Virtual Structures

One nice thing about this topic is that it seemed to resonate with several bloggers who had either strayed away from T-SQL Tuesday or had never participated; hopefully, the bug to write will stick (and I’m pointing the finger at myself for this one as well).

Beginning at the Beginning:

Pinal Dave in his gentle teaching style covers several different questions and answers about JOIN techniques. Great way to review the basics and get conversations started with beginners.

KenJ is a bit esoteric, but a great reminder of what resources there are to learn more about SQL Server.

JOINs In The Real World:

Tracy McKibben demonstrated a very simple tuning tip based on real production experience: the Nested JOIN

Rich Brown reminds us that good query construction often involves understanding how the optimizer handles JOINs under the covers.

Andy Galbraith (Yet Another SQL Andy!) reminds us to Respect Your JOINs. It’s funny how often we assume that database queries are logically well-written when we start looking for performance problems.

Bob Pusateri points out that WHERE clauses influence JOIN behaviors. You have to look at the entire SQL statement to make sure you’re getting what you’re supposed to be getting.

Matt Nelson reminds us that unnecessary JOINs are bad, and sometimes you need to dig a little deeper when performance tuning.

A Little Deeper:

Rob Farley toasted my brain a little on this post about Joins without JOINs.  It’s a well-written explanation of what an Ant-Semi JOIN is.

Brad Schulz finished the cooking job with a take on Semi-JOINs, among other things.  Is Brad really Rob in reverse?

Muthukkumaran Kaliyamoorthy covered the internal join mechanisms, and why the optimizer chooses merge, hash, or nested loop joins.

Robert Matthew Cook has a couple of great metaphors for explaining Merge, Hash, and Nested Loop JOINs.

Wayne Sheffield pointed out some interesting syntactical ways of writing JOINs. I’m not sure if I’m comfortable with some of them, but they may be of some use in certain edge scenarios. Or, if you just want to mess with the guy who reviews your code.

Richard Douglas offers up a short-but-sweet explanation of the relationship of Key Lookups to JOINs.

The Future is a Ticking Time Bomb…

Thomas Rushton points out that Denali may finally force us to clean up our code.

My Portugese is Not Up To Par…

 
Finally, Ricardo Leka wrote a post that I had to use Google Translate to interpret.  I think I lost something in  translation, because I’m not sure how the example relates to JOIN’s, but thought I would include it anyway.  http://leka.com.br/2011/10/04/t-sql-tuesday-23-joins/

Time once again for another edition of T-SQL Tuesday!  What’s that, you say?  Early?  Why yes, indeed.  Due to the potential schedule of conflict of PASS’s Summit 2011 occurring on the second Tuesday of October (the normal date for T-SQL Tuesday), I’ve gotten special permission to bump it up a week. 

To participate in this month’s T-SQL Tuesday, your post must go live between midnight UTC on Tuesday, October 4, 2011 and midnight UTC on Wednesday, October 5.

Your post needs to link back to this blog, and if you use the image, anchor it to this post.  Make sure you leave a comment or a trackback to this post (so I can find it later, when I write up the summary).

Topic d’jour?  JOINS (I’m in a fundamentals mood lately).  Note that I also like creative and esoteric posts, so if you can find a way to apply SQL as a metaphorical language for community activity, I’ll read it and enjoy it.  If you just want to tell me in a simple fashion the difference between a HASH and MERGE join, I’m cool with that, too.

Do me a favor, though, and please spread the word about the early date.  Looking forward to reading your submissions.

SQL Server XML 201

The xml datatype in SQL Server expands the potential of the relational platform to store increasingly complex forms of data, but without the use of the appropriate query language, much of that potential can remain unused. This session will cover the basics of SQL Server XQuery and FLWOR; the assumption is that attendees will have some basic exposure to XML (including the use of XML in SQL Server). Learn how to “run queries within a query”, and how to extract XML data into a tabular format. Coverage will include the five basic XML methods (.exist(), .value(), .query(), .nodes(), and .modify()) and FLWOR (for, let, where, order by, and return).

One idea that I’m really excited about is a change in the monthly meetings for AtlantaMDF (our SQL Server User Group); like most user groups, we have a meet-and-greet followed by a presentation (or two).  The presentations usually cover some mid-level to advanced topic, and usually assume that the attendees have some knowledge with SQL Server.  We’re going to tackle that assumption.

Starting at our next meeting (Monday, September 12), we’re going to present short presentations before the main one that are targeted to new users of SQL Server; the goal is to a) build up our new members, and b) help grow our speaker pool.  I’m excited to present the first topic “Stuff in the FROM clause” on Monday, so if you’re in the Alpharetta area Monday night, come by and see me.

Also coming up is our fourth SQL Saturday (#89); although I haven’t been as involved with the planning on this one as I have in years past, it’s been exciting to see it unfold.  I’m looking forward to presenting a session on XQuery, and hanging out by the user group booth. If you’re gonna be there, stop by and say Hi!

SQL Server XML 201 [Application and Database Development]
Stuart Ainsworth (Gladiator Technology Services)
 
Basic Guidelines for VLDB’s [Enterprise Database Administration and Deployment]
Stuart Ainsworth (Gladiator Technology Services)

VOTE HERE: http://www.sqlpass.org/summit/2011/UserLogin.aspx?returnurl=%2fsummit%2f2011%2fSummitContent%2fCommunityChoice.aspx

Just as an aside, I’d also like to plug a couple of other sessions by some AtlantaMDF members:

Bad SQL [Application and Database Development]
Geoff Hiten (Intellinet)
 
ETL Smackdown: PowerShell vs SSIS — with Aaron Nelson [BI Architecture, Development and Administration Topics]
Julie Smith (Key2 Consulting)
Aaron Nelson (@SQLvariant)

4 out of the 20 sessions being considered for Community Choice are by speakers from my local chapter, which makes me proud. Thanks for your consideration, and more posts to come soon!

Another reason to celebrate?  I got accepted to speak at SQL Saturday 64 (Baton Rouge).  I’m excited to head back home for good food and good times.  I needed a little affirmation after the disappointment over Summit.

Anyway, I may not blog much in the next few weeks; please stay tuned, because good things are happening.