SQL Lesson

A VIEW is a virtual table that is based on the result of a query. It provides a way to simplify complex queries by abstracting the underlying query logic into a reusable object. Views can be used to retrieve data, perform calculations, and even join multiple tables. Creating a View To create a view, you […]

Transaction control statements are used to manage and control the execution of database transactions. A transaction is a logical unit of work that consists of one or more SQL statements. Transaction control statements allow you to ensure data integrity and consistency by defining a set of operations that should be treated as a single atomic

In SQL, you can perform bulk updates and deletes on multiple rows simultaneously by using the UPDATE and DELETE statements in conjunction with joins. This allows you to update or delete data based on relationships between tables. Bulk Updates with JOINs To perform bulk updates using joins, you can use the UPDATE statement along with

INSERT INTO SELECT statement allows you to insert data from one table into another table. This statement is useful when you want to copy data from an existing table or retrieve data from a complex query and insert it into another table. Basic Syntax INSERT INTO target_table (column1, column2, …) SELECT column1, column2, … FROM

The IN and NOT IN operators are used to compare a value against a list of values or the result of a subquery. These operators allow you to perform filtering based on whether a value matches any value in the specified list or subquery. IN Operator The IN operator checks if a value matches any

In SQL, the EXISTS and NOT EXISTS operators are used to check for the existence of rows that meet certain conditions within a subquery. These operators return a boolean value (true or false) based on whether the subquery returns any rows. EXISTS Operator The EXISTS operator checks if a subquery returns any rows. If at

In SQL, scalar subqueries and correlated subqueries are two types of subqueries that allow you to retrieve specific data and perform calculations within a query. Let’s explore the differences between scalar and correlated subqueries and how to use them effectively. Scalar Subqueries A scalar subquery is a subquery that returns a single value. It can

In SQL, subqueries allow you to retrieve data from nested queries. Subqueries, also known as nested queries or inner queries, are queries embedded within another query. They can be used in various parts of a SQL statement, such as the SELECT, FROM, WHERE, and HAVING clauses. Here’s an overview of how to use subqueries to

In SQL, the ALTER TABLE statement is used to modify the structure of an existing table. It allows you to add, modify, or drop columns, as well as make changes to constraints and indexes. Here’s an overview of how to use ALTER TABLE statements to modify table structure. Adding Columns To add a new column

In SQL, the DELETE statement is used to remove one or more rows from a table. It allows you to delete specific records based on specified conditions. Here’s an overview of how to use the DELETE statement to remove data from tables. Basic Syntax The basic syntax of the DELETE statement is as follows: DELETE