After my CTE presentation a while back I was asked many questions, and received several great suggestions from people. One question was how does the performance compare between a recursive CTE to generate a hierarchical tree path listing and a query using self JOINs and UNION ALL to generate similar results. To test this I created a simple table …
Years ago while working on my CTE presentation for a SQL Saturday I added a blog post called “Using a CTE to Split a String Into Rows“, and since that posting I have used it many times. But as things go in development eventually there is a need to do something more. Doing some complex string building to create files …
Using a CTE to Split a String Into Rows with Line Numbers Read more »
The article could be named, “How to use up all of your SQL Server available memory with a single CTE query.” Another name for the article could just be “SQL Server Bug Report” depending on how you look at it. When presenting unleashing Common Table Expressions at SQL Saturday a while back, I was asked a couple of great questions …
The following question came up when working on my CTE presentation for SQL Saturday. Does a query that JOINs a CTE to itself execute the CTE query once or twice? For instance: ;WITH deptCTE(id, department, parent) AS (SELECT id,department,parent FROM Departments)SELECT q1.department,q2.department FROM deptCTE q1 INNER JOIN deptCTE q2 ON q1.id = q2.parent WHERE q1.parent IS NULL; The following execution plan is produced showing that the Departments table is hit twice with a table scan each time with the same cost. …
Common Table Expressions are a great way to simplify complex derived table queries. If it makes sense to break out one derived table or subquery into a CTE, it can make sense to do multiple. To use multiple CTE’s in a single query you just need to: Finish the first CTE Add a comma, Declare the name Optional columns for …
Have you ever wanted to create a recursive query, but didn’t see how to do it. With the Common Table Expressions session you will learn everything needed to start using CTE’s for recursive queries, as temporary views, and to use the result set multiple times in the same query. Learn how simplify query syntax using CTE’s. One of the most …
The following is chapter 7 from my Common Table Expressions book in its entirety. I can remember the first time that I worked on data paging code. I had to page through web site search results 20 at a time on a given web page. My task was to understand how it had been written and to do some bug fixing. After reviewing …
The following is chapter 6 from my Common Table Expressions book in its entirety. READER NOTE: Please run the CTEBookSetup.sql script in order to follow along with the examples in this chapter. The script mentioned in this chapter is available at http://SteveStedman.com. Thinking of the proverb “two heads are better than one” makes me think, it really depends on the people. Two people working together are …
The following is chapter 5 from my Common Table Expressions book in its entirety. READER NOTE: Please run the CTEBookSetup.sql script in order to follow along with the examples in this chapter. The script mentioned in this chapter is available at http://SteveStedman.com. Hierarchical CTEs When looking at the table of contents for a book it is generally represented as an outline of some kind utilizing indentation, …
As part of the CTE book there is a sample database that all the queries use. You can download the create script for that sample database here and run it in your local SQL Server, or on a test SQL Server: Due to the security settings of the web site, and many download checks, I was unable to anme the …