David Durant


Stairway to SQL Server Indexes

Deeper into Nonclustered Indexes: Stairway to SQL Server Indexes Level 2

By this stage, you should be familiar with the basics of SQL Server indexes. We've discussed what an Index actually is, as well as some of the most common types you're likely to encounter. Now that we've seen some simple examples of how Indexes can be useful, we're going to delve deeper into nonclustered indexes, as we'll see how they can improve the performance of more complex queries.

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2022-11-16 (first published: )

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Stairway to SQL Server Indexes

An Introduction to SQL Server Indexes: Stairway to SQL Server Indexes Level 1

Indexes are the database objects that enable SQL Server to satisfy each data access request from a client application with the minimum amount of effort, resulting in the maximum performance of individual requests while also reducing the impact of one request upon another. Prerequisites: Familiarity with the following relational database concepts: Table, row, primary key, foreign key

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2019-03-29 (first published: )

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Stairway to SQL Server Indexes

Pages and Extents: Stairway to SQL Server Indexes Level 4

We've now seen how indexed and non-indexed tables perform in queries, and established "logical reads" as the metric for query performance. Now it is time to explain why logical reads are an excellent metric and also explain what is actually being read.

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2019-03-29 (first published: )

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Question of the Day

Crazy Code I

I have this data in my Customer table:

CustomerID CustomerName
1          Steve
2          Andy
3          Brian
4          Allen
5          Devin
I run this code:
SELECT
  t.CustomerID
, c.value
FROM
  ( SELECT
      CustomerID
    , STRING_AGG (CustomerName, ',') AS me
    FROM customer
    GROUP BY CustomerID) t
  CROSS APPLY STRING_SPLIT(me, ',') c;
What is returned?

See possible answers