MySQL provides us with the ability to create multiple prepared statements and run them as many times as we like, while changing the parameter values with each run.
While prepared statements are only available to the session that created them, they are stored in the server. So it’s quite possible that a server could have a build up of lots of prepared statements hanging around once different users have created them.
Continue readingThere are many ways to find the primary key column in SQL Server, but sometimes we might need to identify the name of the primary key’s index.
For example, we may want to identify the index’s name if we need to disable the primary key for some reason (we disable primary keys by disabling their index).
The query below can help if you need to find the name of a primary key’s index for a given table.
Continue readingIf you’re getting an error that reads “Syntax ‘*’ is not allowed in schema-bound objects” in SQL Server, it appears that you’re using the asterisk wildcard (*) to select all columns when trying to define a schema-bound object (like a schema-bound view).
As the error message states, this is not allowed.
To fix this issue, explicitly name each column.
Continue readingIf you’re getting an error that reads something like “ERROR 1066 (42000): Not unique table/alias: ‘d’” in MySQL, it could be that you’re trying to assign a duplicate alias to a table. Or it could be that you’re doing a self-join without assigning table aliases.
Table names and aliases must be unique when doing queries in MySQL.
The error can also happen if you use HANDLER to open a table, but then try to open it again before closing it.
To fix this issue, be sure to use unique table aliases in your query. And if you’re using HANDLER, either close the table or continue working with it (without trying to open it again).
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.
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