When using PostgreSQL’s psql command line tool, we can use the \dt command to get a list of tables. This meta-command can display all tables, or just tables that match certain patterns. Below is an overview of how \dt works, its options, and examples of its various uses.
Fixing Error 258 “Cannot call methods on nvarchar(max)” When a Subquery Uses FOR XML in SQL Server
If you’re running a subquery that uses FOR XML to produce XML in SQL Server, but you’re getting error 258, which reads “Cannot call methods on nvarchar(max)” it might be that you’re trying to query the XML in the outer query, but your inner query 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 subquery outputs the result using the xml data type.
Continue readingWhat is a Junction Table in SQL?
A junction table, also known as an associative table or a bridge table, is a table used to manage many-to-many relationships between two other tables in a relational database.
In SQL, many-to-many relationships cannot be directly implemented using just two tables because each table’s foreign key can only relate to one other table’s primary key. Instead, a junction table is created to “link” the two tables together.
Continue readingHow to Disable an Index in SQL Server
Disabling an index in SQL Server can be a useful technique to improve the performance of bulk insert operations or when you need to perform maintenance on your database.
This article provides the code/syntax required to disable an index in SQL Server.
Continue readingFix Error “The ORDER BY clause is invalid in views, inline functions, derived tables, subqueries, and common table expressions…” in SQL Server (Error 1033)
If you’re getting an error that reads “The ORDER BY clause is invalid in views, inline functions, derived tables, subqueries, and common table expressions, unless TOP, OFFSET or FOR XML is also specified” in SQL Server, it appears that you’re using the ORDER BY clause in a place that it must also be accompanied by a TOP, OFFSET or FOR XML clause, but you’re not including one of those clauses.
To fix this issue, be sure to include one of those clauses in your query if you need to use the ORDER BY clause.
Ensuring Data Reliability: The Role of Physical Integrity in Database Management
Maintaining the reliability, accuracy, and consistency of data is paramount when dealing with databases. One important factor that plays a huge role in ensuring these qualities is the concept of physical integrity.
While much attention is given to logical integrity—ensuring the data follows the rules of the schema and maintains meaningful relationships—physical integrity is equally important. It deals with the actual storage of data and the correct functioning of the hardware and software systems that store and manage this data.
This article delves into what physical integrity is in the context of database management, why it is important, how it can be compromised, as well as best practices for maintaining it.
Continue readingUsing ON UPDATE SET DEFAULT in SQL Server
In SQL Server, foreign keys are essential for maintaining referential integrity between tables. When creating foreign keys, we have a number options available to us when it comes to defining what should happen in the event that the related data in the parent table changes. One such option is ON UPDATE SET DEFAULT.
This article will explain what this option does, provide an example of its usage, and offer a practical scenario where this feature can be useful.
Continue readingFix “The correlation name … is specified multiple times in a FROM clause” in SQL Server (Error 1011)
If you’re getting an error that reads something like “The correlation name ‘a’ is specified multiple times in a FROM clause’” in SQL Server, it could be that you’re doing a join on two tables, but you’re assigning them the same aliases.
Each table’s alias must be unique.
To fix this issue, be sure to use unique table aliases in your query.
Continue readingIndexes on Expressions in PostgreSQL: A Quick Overview
In PostgreSQL, indexes on expressions (also known as “functional indexes”) allow you to create an index not just on a column but on the result of an expression or function applied to a column (or multiple columns). This can significantly improve query performance when the same expression is used frequently in queries, especially for complex calculations or transformations.
Continue readingConverting Between Uppercase and Lowercase in PostgreSQL
PostgreSQL provides us with a few functions that we can use to convert strings between uppercase and lowercase.
We can convert the whole string to uppercase or lowercase, or we can convert it to initial caps, where the first letter of each word is uppercase and the rest of the word is lowercase.
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