All articles: Data Manipulation Language (DML)

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SQL Server: Fill columns with increment numbers – Querychat
Unique numbers of data in a database table can be created in several ways. One of them is the incremental numbers that generate a sequence of numerical values. A sequence in incremental numbers can be done when creating a table structure with columns given the IDENTITY property. The following is...
Checking an active session history in PL/SQL – Querychat
In this article, we will check how to identify what kind of activity an active session has in PL/SQL by using the Oracle DBA_HIST_ACTIVE_SESS_HISTORY view. A proper database administration makes us know how the database is behaving due to its multiple processing transactions. The DBA_HIST_ACTIVE_SESS_HISTORY is composed of the WRM$_SNAPSHOT,...
MySQL SELECT FOR UPDATE statement – Querychat
In this article, we will discover how to secure your requests. Also, we will learn how to avoid unexpected updates to the requested rows by other users, namely, we will take a look at the SELECT FOR UPDATE statement. SELECT FOR UPDATE syntax We cannot receive enough security with the...
Working with the INSERT … ON DUPLICATE command in MySQL – Querychat
In this article, we will check on how to work with the INSERT … ON DUPLICATE KEY UPDATE command and analyze certain scenarios with simplified examples for them. A basic Insert statement cannot control a duplicate record, especially if the inserted value is directed on a PRIMARY KEY or a...
Working with the CORR function in PL/SQL – Querychat
In this article, we will cover what the CORR function is in PL/SQL, basic knowledge of how it works, including an example of how it will be useful. The CORR function executes the Pearson’s coefficient of correlation (or PCC). First, let us understand what the Pearson’s coefficient of correlation is....
What are SQL Server DATALENGTH and LEN functions – Querychat
This guide is about two functions of SQL Server that are designed to show the length of specified expressions in bytes, namely DATALENGTH and LEN functions. Additionally, we will take a look at the differences between them and how to use each function. SQL Server DATALENGTH function The DATALENGTH function...
What is SQL Fiddle?– Querychat
In this article, we will check what SQLfiddle is, the basics of the tools that it provides, and how it works. Sometimes we do not have access to a local SQL testing engine. SQLfiddle.com is one of the online options to test different SQL versions.  SQL has several online testing...
How to Use the SQLite WHERE Clause – Querychat
In this article, we will learn the SQLite WHERE clause. We will discover why anyone who learns and uses SQLite should know the WHERE clause, and also we will look at the illustrative use examples. SQLite WHERE clause syntax We use the SQLite WHERE clause to filter the data we...
How to Use SQLite INSERT INTO Statement – Querychat
In this article, we will discover what is SQLite INSERT INTO statement and how we can use it in our everyday work. What is more, we will consider several illustrative examples with different use cases. SQLite INSERT INTO syntax We need the INSERT INTO statement to add new records to...
Difference Between GROUP BY and ORDER BY – Querychat
In this article, we will analyze the GROUP BY and ORDER BY clauses and find out what is the difference between these two clauses.  Many people consider GROUP BY and ORDER BY clauses to be similar, but this is not right, let’s look at the syntax. GROUP BY SQL Oracle...
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