What is a Heap in SQL Server?

Posted on by Ian

In SQL Server, a heap is a table without a clustered index. Unlike tables with clustered indexes, which sort data in a specific order, heaps store data in no particular order. That’s because the clustered index is what determines how the table is stored and sorted (it’s sorted on the clustered index’s key column).

If there’s no clustered index, then data is initially stored in the order in which the rows are inserted, although the database engine may change this in order to store the rows more efficiently.

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How to Delete an Index in SQL Server

Posted on by Ian

If you find yourself with an index in SQL Server that you no longer need, you may decide to disable it, or you may opt to get rid of it altogether. That way you can declutter your database, free up space, and perhaps help improve performance of updates to the data.

Typically, to delete an index in SQL Server, we use the DROP INDEX statement. There are cases where we might drop it via other means (for example, if it’s implemented as part of a PRIMARY KEY or UNIQUE constraint – also shown below), but DROP INDEX is usually the go to command for such operations.

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Fix Error 159 “Must specify the table name and index name for the DROP INDEX statement” in SQL Server

Posted on by Ian

If you’re getting SQL Server error 159 that reads “Must specify the table name and index name for the DROP INDEX statement“, it’s probably because you’re trying to drop an index without specifying the table name.

When we drop an index, we must specify both the index name and the table name.

To fix this issue, include both the index name and the table name in your DROP INDEX statement.

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Understanding the Correlated Subquery in SQL

Posted on by Ian

When writing SQL queries, we sometimes find ourselves including a subquery in the query in order to get the results we want. Sometimes the subquery we include could be taken out of that query and run by itself to return its own independent result set. But not the correlated subquery.

A correlated subquery relies on the outer query for its data. We can’t simply move it outside of the outer query and expect it to work.

Let’s take a look the correlated subquery in SQL and observe it in action with a few examples.

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The Difference Between INNER and LEFT JOINs in SQL

Posted on by Ian

SQL joins are fundamental operations in relational databases, allowing us to combine data from multiple tables. Two of the most commonly used join types are INNER JOIN and LEFT JOIN. Understanding the difference between these joins is crucial if you intend to use joins in your queries.

In this article, we’ll look at the difference between the INNER JOIN and LEFT JOIN using a simple example.

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Using the WHERE Clause Effectively: Common SQL Operators and Their Usage

Posted on by Ian

The WHERE clause is a fundamental part of SQL queries that allows us to filter data based on specific conditions. Understanding how to use various operators within the WHERE clause can significantly enhance our ability to retrieve precisely the data we need.

This article explores some of the operators that are most commonly used with the WHERE clause.

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Fix Error 11415 “Object … cannot be disabled or enabled. This action applies only to foreign key and check constraints” in SQL Server

Posted on by Ian

If you’re getting SQL Server error 11415 that reads something like “Object ‘UQ_Employees_Email’ cannot be disabled or enabled. This action applies only to foreign key and check constraints“, it’s probably because you’re trying to disable either a DEFAULT, UNIQUE or PRIMARY KEY constraint.

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Nested WHILE Loops in SQL Server: A Beginner’s Guide with Examples

Posted on by Ian

WHILE loops are a fundamental concept in T-SQL programming, allowing us to execute a block of code repeatedly as long as a specified condition is true. Nested WHILE loops take this concept further by placing one WHILE loop inside another, enabling more complex iterations.

This guide will walk you through the basics of nested WHILE loops in SQL Server, complete with simple examples and a demonstration of the BREAK statement.

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