t-sql

5 Ways to Return UNIQUE Constraints in SQL Server

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In SQL Server, we can use UNIQUE constraints to ensure that a column (or columns) contain only unique values. When we have a UNIQUE constraint against a column, the system will prevent any duplicate values are entered into that column.

Sometimes we need to return a list of UNIQUE constraints, so that we simply know what we’re working with. Other times we might want to create scripts for all of our UNIQUE constraints so that we can recreate the constraints later.

Regardless of the reason, here are five methods for returning UNIQUE constraints in a SQL Server database.

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Understanding the BREAK Keyword in SQL Server WHILE Loops

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WHILE loops are a powerful feature in most programming languages that allow developers to execute a block of code repeatedly as long as a specified condition is true. However, there are times when we may need to exit a loop prematurely based on certain criteria. SQL Server caters for this possibility with the BREAK keyword.

In this article, we’ll explore how to effectively use the BREAK keyword within WHILE loops in SQL Server.

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What is a Clustered Index in SQL Server?

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There are around a dozen types of index in SQL Server, but the most commonly used index type would have to be the clustered index. By default, a clustered index is automatically created when we create a primary key, and so if your tables have primary keys, then there’s a pretty good chance you’ve got clustered indexes all over your database.

But what exactly is a clustered index?

Let’s delve into what a clustered index is, how it works, its relationship with primary keys, and why it’s so important for our database performance.

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What is a Nonclustered Index in SQL Server?

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We’ll often hear SQL Server developers talk about adding indexes to a table to improve the performance of some of the more heavily run queries. Such queries could be quite complex, and/or search through large tables, perhaps with lots of joins, and generally take a long time to complete.

But it’s not just a matter of saying “add an index” and being done with it. We need to decide how to design the index, and even before that, what type of index to add.

Two of the most commonly used index types in SQL Server are the clustered index and the nonclustered index.

In this article, we’ll explore what a nonclustered index is, how it works, and when we should use it to enhance our database performance.

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Fix Error 8655 “The query processor is unable to produce a plan because the index … on table or view … is disabled.

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If you’re getting SQL Server error 8655 that reads something like “The query processor is unable to produce a plan because the index ‘PK__Employee__7AD04FF1A39ECAB1’ on table or view ‘Employees’ is disabled“, it’s probably because the clustered index for the table is disabled.

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How to Disable a Primary Key in SQL Server

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Under most circumstances, disabling a primary key is a bad idea. A very bad idea. After all, we implement primary keys in the name of data integrity, and by disabling a primary key, we could compromise that effort.

But there may be cases where you need to disable a primary key, for one reason or another. For example, to facilitate data migration efforts, or bulk inserts, to perform certain maintenance tasks, or simply to insert dummy data in your development environment.

Whatever the reason, here’s how to disable a primary key in SQL Server.

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How to Change SQL Server’s Default Fillfactor

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Fillfactor is an option that we can set on SQL Server indexes in order to fine tune index data storage and performance. It determines the percentage of space on each leaf-level page to be filled with data, reserving the remainder on each page as free space for future growth.

The default fillfactor can be set as a configuration option. SQL Server sets this value to 0, and so this is what’s used when we create an index without specifying a fillfactor. The value of 0 is actually the equivalent of 100 (or meaning 100%). In other words, by default, the leaf-level pages are filled to capacity.

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Fix Error 8111 “Cannot define PRIMARY KEY constraint on nullable column in table” in SQL Server

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If you’re getting SQL Server error 8111 that reads something like “Cannot define PRIMARY KEY constraint on nullable column in table ‘Employees’“, it’s probably because you’re trying to add a PRIMARY KEY constraint to an existing column that is nullable. In other words, the column isn’t defined with a NOT NULL constraint.

We can only add primary keys to columns that are defined as NOT NULL.

To fix this issue, define the table as NOT NULL before attempting to add the primary key.

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Fix Error “Either the parameter @objname is ambiguous or the claimed @objtype (INDEX) is wrong” in SQL Server

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If you’re getting SQL Server error Msg 15248 that reads something like “Either the parameter @objname is ambiguous or the claimed @objtype (INDEX) is wrong’“, it appears that you’re trying to perform an operation on an index, but you’ve got the naming syntax slightly wrong. Perhaps you’re trying to rename it.

When we do stuff like rename an index, we need to include the table name when referring to the existing index. It’s possible that you’ve not included this in your code.

To fix this issue, be sure to include the table name.

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