Tag: indexes

Fix Error 1987 “Cannot alter nonclustered index … because its clustered index is disabled” in SQL Server

Posted on by Ian

If you’re getting SQL Server error 1987 that reads something like “Cannot alter nonclustered index ‘UQ_Employees_Email’ on table ‘Employees’ because its clustered index is disabled“, it’s probably because you’re trying to rebuild a nonclustered index when the clustered index for the table is disabled.

To fix this issue, either enable/rebuild the table’s clustered index first, then try again, or enable all indexes at once.

The clustered index will typically be the primary key index (unless you’ve specified another clustered index for the table).

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Understanding Filtered Indexes in SQL

Posted on by Ian

In SQL, indexing can be a great way to improve query performance across our database. We can create indexes to support the most commonly used queries, and these indexes can help our queries run much faster.

But it’s not always a matter of just “adding an index” and leaving it at that. If we really want the best bang for our buck, we usually need to look at how best to implement the index. There are many decisions that go into designing the best index for the job. And one such decision might be, should this be a filtered index?

But what exactly is a filtered index, and how can it improve our database efficiency?

Let’s find out.

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Fix Error 1505 “The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name” in SQL Server

Posted on by Ian

If you’re getting an error that reads something like “The CREATE UNIQUE INDEX statement terminated because a duplicate key was found for the object name” it’s probably because you’re trying to create a UNIQUE constraint on a column that already contains duplicate values.

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Introduction to Indexing in SQL

Posted on by Ian

When working with databases, performance can be very important. This is especially true in production environments where the end users expect their queries and reports to be generated within seconds (or even milliseconds).

While blistering fast queries may be the norm with smaller datasets, as our databases grow larger and more complex, it can become much more of a challenge to keep our queries nice and snappy. When working with smaller datasets, it’s often possible to get lightning speed results even when not optimizing for speed. But as the datasets grow larger, we need more efficient tools and techniques to retrieve and manipulate data. One such tool is the index.

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How to Hide a GIPK from the SHOW CREATE TABLE Statement (and SHOW COLUMNS and SHOW INDEX) in MySQL

Posted on by Ian

When we have a table with a generated invisible primary key (GIPK) in MySQL, we can usually see its definition when we use various SHOW statements such as SHOW CREATE TABLE, SHOW COLUMNS, and SHOW INDEX, as well as when we query information schema tables such as information_schema.columns.

But there is a way of hiding the GIPK from such statements. It all comes down to the show_gipk_in_create_table_and_information_schema variable. Yes, there’s actually a system variable that allows us to hide GIPKs from the output of various SHOW statements and information schema tables.

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How to Check Whether an Index is Hidden in MongoDB

Posted on by Ian

From MongoDB 4.4, it’s possible to hide an index from the query planner. This allows you to evaluate the potential impact of dropping an index without actually dropping the index.

You can use the getIndexes() method to check whether or not an index is hidden. If an index is hidden, that index will display a hidden field as having a value of true (i.e. "hidden" : true).

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