SQL Server – Dissect the Internals of sp_spaceused

This article is an effort to dissect the output of the sp_spaceused stored procedure.

Introduction

Understanding the database usage internals and the growth trends play a vital role in the defining the right sizing of the database. sp_spaceused is probably an administrator’s most widely-executed system stored procedure to find the disk space used by a database. This helps get a quick glimpse of the database usage. statistics. sp_spaceused is used to display the number of rows, the data size, index size, amount of used space, unused space by each object, and the unallocated size of the database. Although looking at the values given by sp_spaceused, one shouldn’t think of shrinking the database or data file or log file. Many a time, we are unaware of what we are doing. Many a time, we don’t know what would be the aftereffects of doing such resource intrinsic operations. The output of sp_spaceused tells us a lot about the current performance of the database. The unallocated column and the unused column tell us the free space left at the database and the table levels. Read More

SQL Server Triggers: Understanding and Alternatives

The SQL Server trigger is a special type of stored procedures that is automatically executed when an event occurs in a specific database server. SQL Server provides us with two main types of triggers: the DML Triggers and the DDL triggers. The DDL triggers will be fired in response to different Data Definition Language (DDL) events, such as executing CREATE, ALTER, DROP, GRANT, DENY, and REVOKE T-SQL statements. The DDL trigger can respond to the DDL actions by preventing these changes from affecting the database, perform another action in response to these DDL actions or recording these changes that are executed against the database. Read More

Creating Dynamic Pivot Table with QUOTENAME Function

In my previous article on the basic pivot operator, we saw how pivot operator could be used to convert rows to columns, resulting in pivot tables. We saw that there were three main steps to create a pivot table. The first step was selecting the base data. The second step was converting the base data to a table-valued expression, and the final step involved applying a pivot operator to the temporary data, which resulted in the pivot table.

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Methods to Rank Rows in SQL Server: ROW_NUMBER(), RANK(), DENSE_RANK() and NTILE()

SQL Server provides us with a number of window functions that help us to perform calculations across a set of rows, without the need to repeat the calls to the database. Unlike the standard aggregate functions, the window functions will not group the rows into a single output row, they will return a single aggregated value for each row, keeping the separate identities for those rows. The Window term here is not related to the Microsoft Windows operating system, it describes the set of rows that the function will process.

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Counting references to a record in a table via Foreign Keys

I have recently needed to solve the task for my own purpose: to calculate the number of external records linked by a foreign key for each record in a table (File). The task was solved for the specific structure of the File table, but if necessary, the solution can be reworked to a universal one.

I’ll clarify that the solution was developed for an unloaded database, without millions of records and an every minute update, so there was not much concern about the performance.

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Introducing Common Table Expressions in SQL Server

Common Table Expressions, or CTE for short, is simply a technique to create a temporary set of records that can be referenced within an INSERT, SELECT, UPDATE or DELETE statement.

Common table expressions were introduced by Microsoft in SQL Server 2005. They are not stored as objects in the database memory as their lifespan is equal to the execution time of the query. As soon as a query completes they are removed from the database memory. CTE can be referenced in a query as many times as you want and they can also be self-referencing.

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Introduction to Temporary Tables in SQL Server

A temporary table in SQL Server, as the name suggests, is a database table that exists temporarily on the database server. A temporary table stores a subset of data from a normal table for a certain period of time.

Temporary tables are particularly useful when you have a large number of records in a table and you repeatedly need to interact with a small subset of those records. In such cases instead of filtering the data again and again to fetch the subset, you can filter the data once and store it in a temporary table. You can then execute your queries on that temporary table. Temporary tables are stored inside “tempdb” which is a system database. Let’s take a look at how you can use a temporary data in a simple scenario.

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