Database Management Systems
If you work with MySQL databases, you may have encountered the SERIAL type in a table’s definition. And if you’ve come over from PostgreSQL, you might have a false expectation about how MySQL’s SERIAL works – unless you already know 😉
Below is a quick overview of MySQL’s SERIAL type, including an explanation of how it differs from PostgreSQL’s SERIAL type and similar functionality from other DBMSs.
There are several ways that we can list all indexes in PostgreSQL. These include utilizing various system catalog views and psql commands. Below are five options for returning a list of indexes in PostgreSQL, along with examples of how to filter the results by index name, table name, and other criteria.
Sometimes when working with SQL Server, we need to get a quick list of indexes on a given table.
Here are three queries that return all indexes on a given table in SQL Server.
Continue readingDisabling constraints in SQL Server can be useful for various operations, such as bulk data loading or certain maintenance tasks. But not all constraints are created equal. The method we use to disable a constraint, and whether that’s even possible, depends on the type of constraint.
In this article, we’ll explore how to disable different types of constraints and consider the potential impacts.
Continue readingIf you’re trying to use a common table expression (CTE) that produces XML in SQL Server, but you’re getting error 4121, which reads something like “Cannot find either column “EmployeeData” or the user-defined function or aggregate “EmployeeData.query”, or the name is ambiguous” it might be that you’re trying to query the XML in the outer query, but your CTE isn’t outputting the XML as an actual xml type.
The FOR XML result must be an xml type in order to process the result on the server.
To fix this issue, make sure the CTE outputs the result using the xml data type.
Continue readingIf 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.
Continue readingDynamic 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.
Continue readingIf you’ve been working with prepared statements in PostgreSQL, you may get to a point where you no longer need one or more of them. In that case, you might want to remove them, or delete them, drop them, or however you want to say it.
Fortunately, this is one of the quickest, easiest things to do in PostgreSQL.
Continue readingA 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.
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.
Continue reading