Primary Key in SQL Database Tutorial

Identifying a suitable primary key is one of the most critical decisions you will have to make. The underlying objective of a primary key is simple and straightforward. A primary key plays a two-pronged fundamental role. At each waking moment in our day, we are literally surrounded by primary keys in a database world, and yet we take them for granted.
 

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Introduction to Structured Query Language SQL pdf

SQL stands for Structured Query Language. SQL is a scripting language expected to store, control, and inquiry information put away in social databases. The main manifestation of SQL showed up in 1974, when a gathering in IBM built up the principal model of a social database. The primary business social database was discharged by Relational Software later turning out to be Oracle.

Models for SQL exist. In any case, the SQL that can be utilized on every last one of the major RDBMS today is in various flavors. This is because of two reasons:

1. The SQL order standard is genuinely intricate, and it isn’t handy to actualize the whole standard.

2. Every database seller needs an approach to separate its item from others.

Right now, contrasts are noted where fitting.

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List of Available Database for Current User In SQL Server

Introduction

When working in the SQL Server, we may have to check some other databases other than the current one which we are working. In that scenario we may not be sure that does we have access to those Databases?. In this article we discuss the list of databases that are available for the current logged user in SQL Server

Get the list of database

Conclusion

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SQL Tutorial - Full Database Course for Beginners. DO NOT MISS!!!

In this course, we’ll be looking at database management basics and SQL using the MySQL RDBMS.
⭐️ Contents ⭐
⌨️ (0:00) Introduction
⌨️ (2:36) What is a Database?
⌨️ (23:10) Tables & Keys
⌨️ (43:31) SQL Basics
⌨️ (52:26) MySQL Windows Installation
⌨️ (1:01:59) MySQL Mac Installation
⌨️ (1:15:49) Creating Tables
⌨️ (1:31:05) Inserting Data
⌨️ (1:38:17) Constraints
⌨️ (1:48:11) Update & Delete
⌨️ (1:56:11) Basic Queries
⌨️ (2:08:37) Company Database Intro
⌨️ (2:14:05) Creating Company Database
⌨️ (2:30:27 ) More Basic Queries
⌨️ (2:26:24) Functions
⌨️ (2:45:13) Wildcards
⌨️ (2:53:53) Union
⌨️ (3:01:36) Joins
⌨️ (3:11:49) Nested Queries
⌨️ (3:21:52) On Delete
⌨️ (3:30:05) Triggers
⌨️ (3:42:12) ER Diagrams Intro
⌨️ (3:55:53) Designing an ER Diagram
⌨️ (4:08:34) Converting ER Diagrams to Schemas
📺 The video in this post was made by freeCodeCamp.org
The origin of the article: https://www.youtube.com/watch?v=HXV3zeQKqGY&list=PLWKjhJtqVAblfum5WiQblKPwIbqYXkDoC&index=8
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SQL Primary Key Example | Primary Key in SQL Tutorial

SQL primary key is a field in a table that is used for uniquely identifying a row in a table. If the column has a primary key constraint, then it will contain unique values and will not able to contain any NULL values. A primary key length cannot exceed more than 900 bytes.

SQL PRIMARY KEY

SQL PRIMARY KEY constraint uniquely identifies each row in the table. Primary keys must contain UNIQUE values, and cannot contain the NULL values. The table can have only ONE primary key; and in the table, that primary key can consist of the single or multiple columns (fields).

A  table will contain only one primary key, which may consist of single or multiple fields, and when multiple fields are used as a primary key, then it is known as composite keys.

If the table has a primary key defined in any of the fields, then it cannot have two or more records having the same values.

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System Databases in SQL Server

Introduction

In SSMS, we many of may noticed System Databases under the Database Folder. But how many of us knows its purpose?. In this article lets discuss about the System Databases in SQL Server.

System Database

Fig. 1 System Databases

There are five system databases, these databases are created while installing SQL Server.

• Master
• Model
• MSDB
• Tempdb
• Resource

Master

• This database contains all the System level Information in SQL Server. The Information in form of Meta data.
• Because of this master database, we are able to access the SQL Server (On premise SQL Server)

Model

• This database is used as a template for new databases.
• Whenever a new database is created, initially a copy of model database is what created as new database.

MSDB

• This database is where a service called SQL Server Agent stores its data.
• SQL server Agent is in charge of automation, which includes entities such as jobs, schedules, and alerts.

TempDB

• The Tempdb is where SQL Server stores temporary data such as work tables, sort space, row versioning information and etc.
• User can create their own version of temporary tables and those are stored in Tempdb.
• But this database is destroyed and recreated every time when we restart the instance of SQL Server.

Resource

• The resource database is a hidden, read only database that holds the definitions of all system objects.
• When we query system object in a database, they appear to reside in the sys schema of the local database, but in actually their definitions reside in the resource db.

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