All articles: General SQL

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How to Set NLS_DATE_FORMAT for the Session in Oracle – Querychat
In this article, we will discover what is NLS in Oracle. We will learn what this acronym stands for and what the NLS data format is. Also, we will get to know how it can be set in Oracle for the user session. NLS in Oracle: what is it? NLS...
How to Backup a Database in SQLite – Querychat
In this article, we learn how to backup SQLite databases. We will learn various methods, such as copying the database file through the Windows Command Prompt (cmd), also using the COPY, BACKUP, and CLONE commands. Always backing up our database is one of the most important routines to anticipate all...
SQL Server restore database with STOPAT option – Querychat
For database recovery, we can use RESTORE DATABASE commands with various options to restore a database from the backup files. One of them is the point-in-time option called STOPAT. In this article, we will learn together on how to recover a database in SQL Server using restore commands with the...
SQL Server sparse columns – Querychat
SQL Server since 2008 edition provides a new feature called sparse columns, which is a type of column that optimizes the storage of NULL or zero values. When a column contains a large amount of NULL or zero values, defining the column as sparse can reduce significant disk space or...
Working with table templates in MySQL – Querychat
In this article, we will learn how to create a table template and tables based on a MySQL database template, using the MySQL Workbench tool, including examples for better understanding. While creating our EER (Enhanced Entity-relationship) model, we create a different kind of tables; master tables, transactional ones and even...
What is PostgreSQL ROLLBACK Command? – Querychat
In this article, we will discover the PostgreSQL ROLLBACK command, when to use this command, and also, for a better understanding, we will consider the concept of transactions. Transactions in PostgreSQL To make things more clear, let’s begin with the definition of the transaction in PostgreSQL. A transaction is a...
What are Sequences in PostgreSQL? – Querychat
In this article, we will discover what sequences are in PostgreSQL and how we can use them in our work. Also, we will analyze the features of its syntax in detail and look at the examples. Sequences In PostgreSQL Sequences in PostgreSQL are similar to auto_increment fields in MySQL, but...
What is Cardinality in SQL – Querychat
In this article, we will discuss the definition of cardinality, where this term can be applied, and we will find out what types of cardinality exist. Also, we will look at the example table showing the different types of cardinality. The meaning of SQL cardinality When this term is used...
SQL Server Reserved Words – Querychat
In this article, we will discover what happens when we use the SQL Server reserved words as our identifiers, how to avoid errors and recommendations when dealing with Transact SQL keywords.  What are SQL Server reserved keywords? Reserved words are called this way because they are directly used in Transact-SQL....
Managing Prefix Indexes in MySQL – Querychat
In this article, we will cover how to manage prefix indexes in MySQL, including simplified examples for better understanding. As a basic rule, we use indexes to optimize table-searching operations. Depending on how the table was created, one or several columns can be used as indexes to access records efficiently. ...
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