Author: Ian

Fix “Unknown table … in HANDLER” in MySQL (Error 1109)

Posted on by Ian

If you’re getting MySQL error 1109 which reads something like “1109 (42S02): Unknown table ‘products’ in HANDLER” in MySQL, it appears that you’re trying to reference a table that’s not currently open when using MySQL’s HANDLER statement.

This can happen when you try to read from a table that you haven’t yet opened. It can also happen when you’ve assigned an alias to the table but you try to reference it without the alias. And it can happen if you try to close a table that isn’t actually open.

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4 SQL Server Dynamic Management Views That Return Memory Usage Data

Posted on by Ian

Dynamic Management Views (DMVs) in SQL Server can be quite handy for monitoring and troubleshooting database performance. When it comes to memory management, understanding how our SQL Server instance uses memory can help us identity performance issues, as well as potential fixes.

In this article, we’ll explore four essential DMVs that provide valuable insights into memory usage in SQL Server.

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Understanding the Different Types of Keys in SQL

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Probably the most widely known key type in SQL is the primary key, which is chosen to uniquely identify each row in a table. Perhaps next is the foreign key, which is used to establish a relationship between tables.

But there are more key types than this, and the differences between them can be subtle, but important. Here we’ll look at nine of the various key types in SQL.

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Using the ORDER BY Clause Inside a CTE Query in SQL Server

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A common table expression (CTE) in SQL Server is used to create a temporary result set that can be referenced within a SELECT, INSERT, UPDATE, or DELETE statement. A CTE can simplify complex queries and improve readability. However, there are specific rules for using the ORDER BY clause inside a CTE.

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Fix “Column names in each table must be unique…” in SQL Server (Error 2705)

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If you’re getting an error that reads something like “Column names in each table must be unique. Column name ‘c1’ in table ‘t1’ is specified more than once” in SQL Server, it appears that you’re trying to create a table with duplicate column names, or you’re trying to add a column to a table that already has a column of that name.

Column names must be unique within each table.

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Possible Reason You’re Getting Error 156 When Running a Subquery in SQL Server

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Error 156 in SQL Server is a generic error that doesn’t tell us much, other than the fact that we’re using the wrong syntax.

But if you’re running a subquery, and you’re getting error 156, which reads “Incorrect syntax near the keyword ‘WHERE’.” or whatever keyword it’s near, it could be that you haven’t declared an alias for the subquery.

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How to Create a UNIQUE Constraint in MySQL

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In MySQL, a UNIQUE constraint is a constraint type that ensures that all values in a column or a group of columns are distinct from each other. In other words, all values that go into the column or group of columns must be unique.

UNIQUE constraints can be applied whenever we want to prevent duplicate entries in specific columns without making them a primary key.

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JOIN ON vs USING vs NATURAL JOIN: What’s the Difference?

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Probably the most common way to join tables in SQL is with the ON clause. But that’s not the only way.

We can also join with the USING clause, which can be more concise, while providing the same or similar results. And there’s also the concept of a natural join, which is more concise again.

Let’s take a look at these three join options and compare them side by side.

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Using the OUTPUT Clause To Log the Result of a MERGE Operation in SQL Server

Posted on by Ian

The MERGE statement is a versatile feature introduced in SQL Server 2008 that allows the combination of INSERT, UPDATE, and DELETE operations into a single statement. When paired with the OUTPUT clause, it becomes even more powerful by enabling us to capture the results of these actions, providing us visibility into what changes occurred during the merge.

In this article, we’ll walk through an example that uses the OUTPUT clause during a MERGE operation in SQL Server.

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