https://informativedataanalyst.blogspot.com/2025/07/data-database.html
Imagine you have a big toy box. Inside, you keep many small boxes. Each small box has different types of toys—cars, animals, blocks, etc. Let’s use this as an example to explain “data” and “database” in SQL.
-
Data: These are like your toys! Each toy is a tiny piece of information. For example, you have a red car, a blue car, and a yellow dinosaur. Each toy has colors, shapes, and types—these details are “data.”
-
Data can be anything and everything Any information or facts can be considered as data like your name, age, Date of birth, Address, mobile no all this stuff can be considered as data.
-
Data can be in any form like it can be in image format, it can be in video format or can be files and txt it can be anything and can be stored in database
DATABASE: This is like your toy box. It’s a place where you keep all your toys (data) so you can find them easily when you want to play. The box keeps everything neat and tidy.
Database can be considered as container where data or information can be stored which is electronically stored in database.
Database are systems that allows users to store and organize the data. They are useful when dealing with large amounts of data.
A database is an organized collection of data, stored and retrieved digitally from a remote or local computer system. Databases can be vast and complex, and such databases are developed using fixed design and modelling approaches.
FOR EXAMPLE. :- College Database organizes the data about the admin, staff, students and faculty etc.
FOR EXAMPLE :- Suppose we have to design college timesheet data that can be stored is staff data, college data, student’s data like student’s details, marks, timesheet any many more.
- SQL: This is like asking your mom or dad to help you find a toy. When you say, “Can you please give me the blue car?”—that’s like using SQL to ask the database for certain information.
So:
- Data = The toys (information).
- Database = The toy box (where you keep all your toys).
- SQL = The way you ask for the toy you want (asking for info).
Purpose of storing data is that it can be easily accessed, manged, modified, protected and can be analysed.
Any information that you entered is actually stored in database. And data is shown in application actually being retrieved from database.
Using the database, you can easily retrieve, insert, and delete the information.
There are various types of databases used for storing different varieties of data:
Centralized database management system is the system in which all the data is stored and managed in a single unit. This is also known as central computer database system. This system is mostly used in an organization.
It comforts the users to access the stored data from different locations through several applications
Unlike a centralized database system, in distributed systems, data is distributed among different database systems of an organization. These database systems are connected via communication links. Such links help the end-users to access the data easily. Examples of the Distributed database are Apache Cassandra, HBase, Ignite, etc.
This database is based on the relational data model, which stores data in the form of rows(tuple) and columns(attributes), and together forms a table(relation). A relational database uses SQL for storing, manipulating, as well as maintaining the data.
Examples of Relational databases are MySQL, Microsoft SQL Server, Oracle, etc.
Non-SQL/Not Only SQL is a type of database that is used for storing a wide range of data sets. It is not a relational database as it stores data not only in tabular form but in several different ways.
It came into existence when the demand for building modern applications increased. Thus, NoSQL presented a wide variety of database technologies in response to the demands. We can further divide a NoSQL database into the following four types:
A type of database where data is stored in a virtual environment and executes over the cloud computing platform. It provides users with various cloud computing services (SaaS, PaaS, IaaS, etc.) for accessing the database.
There are numerous cloud platforms, but the best options are:
Amazon Web Services(AWS) , Microsoft Azure , Kamatera , PhonixNAP , ScienceSoft , Google Cloud SQL, etc.
https://informativedataanalyst.blogspot.com/2025/07/what-are-schemas-in-sql-organizing-data.html
A schema in SQL is like a folder inside a database that helps organize your data. It holds related things like tables, views, and other objects — kind of like how a folder holds files on your computer.
Schema = A named container inside a database that organizes related tables and other objects.
You have a big toy box. Inside the toy box, you keep different kinds of toys — 🚗 cars, 🧸 dolls, 🧱 blocks, 🐶 animals.
Now, you want to organize them so it’s easy to find your favorite toy.
So you say:
- Cars go in Box 1
- Dolls go in Box 2
- Blocks go in Box 3
Each box has a name and holds one kind of toy.
- The big toy box = Database
- Each box inside = Schema
- Inside each schema, we have Tables (the toys), which contain Rows (the actual toy data)
So it's like:
Database ➡️ Schema ➡️ Table ➡️ Rows
DBMS is pronounced as Database Management System
Lot of people consider database as DBMS but it is not correct. Database is act as container that is use to stored data on other hand DBMS is nothing but Database management system is a software which is used to manage the database.
For example: MySQL, Oracle, SQL SERVER etc are a very popular commercial database which is used in different applications.
DBMS provides an interface to perform various operations like database creation, storing data in it, updating data, creating a table in the database and a lot more.
It provides protection and security to the database In the case of multiple users, it also maintains data consistency.
RDBMS stands for Relational Database Management System.
All modern database management systems like SQL, MS SQL Server, IBM DB2, ORACLE, My-SQL, and Microsoft Access are based on RDBMS.
It is called Relational Database Management System (RDBMS) because it is based on the relational model introduced by E.F. Codd.
- Data is represented in terms of tuples (rows) in RDBMS.
- A relational database is the most commonly used database. It contains several tables, and each table has its primary key.
- Due to a collection of an organized set of tables, data can be accessed easily in RDBMS.
Everything in a relational database is stored in the form of relations. The RDBMS database uses tables to store data. A table is a collection of related data entries and contains rows and columns to store data.
Each table represents some real-world objects such as person, place, or event about which information is collected. The organized collection of data into a relational table is known as the logical view of the database.
A row of a table is also called a record or tuple. It contains the specific information of each entry in the table. It is a horizontal entity in the table. For example, The above table contains 5 records.
A column is a vertical entity in the table which contains all information associated with a specific field in a table. For example, "name" is a column in the above table which contains all information about a student's name.
DBMS and RDBMS both are used to store information in physical database but there are some remarkable differences between them.
SQL is a short-form of the Structured Query Language, and it is pronounced as S-Q-L or sometimes as See-Quell.
SQL is a programming language which is used to interact with relational database or RDBMS
It is an database language that is mainly designed for maintaining the data in relational database management systems (RDBMS). It is a special tool used by data professionals for handling structured data
Using SQL commands, you can read data from a relational database or write data into a relational database. You can also create, modify and delete database. SQL can also be used to analyze and protect data.
Almost all of the RDBMS available today such as Oracle, MySQL, Microsoft SQL Server, PostgreSQL, IBM DB2, SQLite, MariaDB, Teradata, Hive etc uses SQL to manage data.
SQL Server provides two types of database:
- System databases
- User Databases
The system databases are created automatically while installing the ANY RDBMS like my sql, sql server on our system. It plays an essential role in the server such database run perfectly.
The following are the list of system databases in SQL Server:
- Master
- Model
- MSDB
- Tempdb
The user databases are created by database users like DBAs and testers who can access a database also.
SQL commands are instructions. It is used to communicate with the database. It is also used to perform specific tasks, functions, and queries of data. SQL can perform various tasks like create a table, add data to tables, drop the table, modify the table, set permission for users. SQL Server provides two types of database:
There are five types of SQL commands: DDL, DML, DCL, TCL, and DQL.
DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc.
Used to define the structure of database objects such as tables, views, functions etc. Using DDL commands, we can create, modify and drop any database objects. The commands include:
All the command of DDL are auto-committed that means it permanently save all the changes in the database.
Here are some commands that come under DDL:
- CREATE
- ALTER
- DROP
- TRUNCATE
create command is used to Create a new database object such a tables, views or functions etc.
To run tests, run the following command
Create database database_name;In the above syntax, the database_name indicates the name of a new database.
Let us understand how to create a database in SQL through an example. To do this, first, open the RDBMS Here we had taken RDBMS sql server after that connect with the database engine by giving the server address and the authentication details. Then, click a new query from the standard bar.
Once the connection becomes successful, execute the below statement to create a new database named Practice:
Create database Practice;Whether, you create a database graphically using the designer or, using a query, the following 2 files gets generated.
.MDF file (Master data File)-
Data File (Contains actual data)
.LDF file (Log Data File)
Transaction Log file (Used to recover the database)
https://github.com/Shubham3016/Sql-Server-Bootcamp/blob/main/1.%20Databases%20in%20Sql%20server.sql
A table enables the user to store data and display information in the database. It arranges the data in rows and columns.
It can have several rows and columns, and each column has a data type associated with it that specifies the type of data it can store, such as numbers, strings, or temporal data.
CREATE TABLE Student(
Id INT IDENTITY PRIMARY KEY,
Name VARCHAR(65) NOT NULL,
Gender VARCHAR(20),
Age INT,
Marks INT
) In the above statement, we have created a 'Student' table.
This table contains five columns Id, Name, Gender, Age, and Marks.
Here, we have defined the id column as a primary key. The IDENTITY data type generates integer numbers that automatically begin with one and increase by one for each new row.
While creating tables there are 2 major components that plays the main role that is DATA TYPES and constraints
Lets start with DATA TYPES SQL Server supports the following data type’s categories:
| Data Type Category | MySQL | PostgreSQL | Oracle | MSSQL | SQLite |
|---|---|---|---|---|---|
| Integer | TINYINT, SMALLINT, MEDIUMINT, INT, BIGINT | SMALLINT, INTEGER, BIGINT | NUMBER(precision), INTEGER | TINYINT, SMALLINT, INT, BIGINT | INTEGER |
| Decimal/Floating | DECIMAL, NUMERIC, FLOAT, DOUBLE | NUMERIC, DECIMAL, REAL, DOUBLE PRECISION | NUMBER(p,s), FLOAT, BINARY_FLOAT, BINARY_DOUBLE | DECIMAL, NUMERIC, FLOAT, REAL | REAL, NUMERIC |
| Character | CHAR, VARCHAR, TEXT | CHAR, VARCHAR, TEXT | CHAR, VARCHAR2, CLOB | CHAR, VARCHAR, TEXT | TEXT |
| Date/Time | DATE, DATETIME, TIMESTAMP, TIME | DATE, TIME, TIMESTAMP, INTERVAL | DATE, TIMESTAMP, TIMESTAMP WITH TIME ZONE | DATE, DATETIME, DATETIME2, SMALLDATETIME | DATE, DATETIME, TIMESTAMP (stored as TEXT) |
| Boolean | BOOL, BOOLEAN (alias for TINYINT) | BOOLEAN | NUMBER(1) or use custom types | BIT | No native BOOLEAN, uses INTEGER 0/1 |
| Binary | BINARY, VARBINARY, BLOB | BYTEA | BLOB, RAW | BINARY, VARBINARY, IMAGE | BLOB |
| UUID/GUID | CHAR(36), BINARY(16) (manual) | UUID | RAW(16) | UNIQUEIDENTIFIER | No native support (stored as TEXT) |
| JSON | JSON, JSONB (MySQL 5.7+) | JSON, JSONB | CLOB with JSON validation | NVARCHAR(MAX) with JSON support | TEXT (no native JSON) |
- Exact numeric: bit, tinyint, smallint, int, bigint, decimal, numeric, money and smallmoney
- Approximate numeric: Read and float
- Date and time: date, DateTime, datetime2, datetimeoffset, smalldatetime, time
- Character strings: char, varchar, text
- Unicode character strings: Nchar, Nvarchar, Ntext
- Binary strings: Binary, image and varbinary
- Other data types: Cursor, hierarchyid, sql_variant, table, rowversion, uniqueidentifier, XML, Spatial and geography
https://github.com/Shubham3016/Sql-Server-Bootcamp/tree/main/Data%20Types
## ALTER
- Alter is used to modify the structure of an existing table.
- Alter can be used to rename a table or rename a column.
- Alter can also be used to add new column or change the data type of an existing column.
- Using Alter we can also add new constraints or remove a constraint from a table.
#### SYNTAX
```bash
Alter database DatabaseName Modify Name = NewDatabaseName
To run tests, run the following command
Alter database Practice Modify Name = DemoAlternatively, you can also use system stored procedure
Execute sp_renameDB 'Practice','Demo'Drop command is use to Delete or Drop a database.
When we remove the database, it will also Permanently delete all the tables, indexes, and constraints.
User have to be very careful while dropping the database because it will lose all the data available in the database.
DROP database Practice Dropping a database, deletes the LDF and MDF files.
TRUNCATE command is used to removes all rows from the table or specified partition without removing the table structure.
TRUNCATE TABLE TABLE_NAME A detailed reference of all major types of operators used in Relational Database Management Systems (RDBMS) such as MySQL, Oracle, SQL Server, PostgreSQL, and SQLite. This guide covers explanations, practical SQL examples, and theoretical relational algebra operators.
- Arithmetic Operators
- Comparison (Relational) Operators
- Logical Operators
- Bitwise Operators
- Compound Operators (Assignment)
- Special Operators
- Set Operators
- String Operators
- Relational Algebra Operators
- Sample SQL Queries
- Notes
Perform mathematical calculations on numeric data.
| Operator | Description | Example |
|---|---|---|
+ |
Addition | SELECT price + tax AS total FROM sales; |
- |
Subtraction | SELECT balance - fee AS net FROM account; |
* |
Multiplication | SELECT quantity * price AS total FROM order; |
/ |
Division | SELECT salary / 12 AS monthly FROM employee; |
% |
Modulo (remainder) | SELECT 10 % 3 AS result; |
Compare values and filter data.
| Operator | Description | Example |
|---|---|---|
= |
Equal to | WHERE status = 'Active' |
<> or != |
Not equal to | WHERE city <> 'Delhi' |
< |
Less than | WHERE age < 30 |
> |
Greater than | WHERE salary > 50000 |
<= |
Less than or equal to | WHERE age <= 18 |
>= |
Greater than or equal to | WHERE fee >= 100 |
Combine or invert multiple conditions.
| Operator | Description | Example |
|---|---|---|
AND |
All conditions true | WHERE dept = 'HR' AND age > 30 |
OR |
Any condition true | WHERE dept = 'Sales' OR dept = 'IT' |
NOT |
Reverse condition | WHERE NOT city = 'Mumbai' |
Operate at the binary level (mostly relevant in SQL Server, less so in MySQL/Postgres).
| Operator | Description | Example |
|---|---|---|
& |
Bitwise AND | WHERE permissions & 1 = 1 |
| |
Bitwise OR | WHERE flags | 2 = 2 |
^ |
Bitwise XOR | SELECT 5 ^ 3 AS result; |
~ |
Bitwise NOT | SELECT ~8 AS result; |
<< |
Left Shift | SELECT 1 << 2 AS shifted_value; |
>> |
Right Shift | SELECT 8 >> 2 AS shifted_value; |
Perform operation and assign result (common in SQL Server and Oracle).
| Operator | Description | Example |
|---|---|---|
+= |
Add and assign | SET @balance += 100 |
-= |
Subtract and assign | SET @count -= 1 |
*= |
Multiply and assign | SET @total *= 2 |
/= |
Divide and assign | SET @avg /= 5 |
SQL constraints are rules that help keep your database clean, correct, and safe. They make sure your data follows certain rules and prevent mistakes like missing values or duplicates.
If you want to make sure that wrong data is not inserted into your table then these kind of sanity checks can be applied by using CONSTRAINTS.
Constraints can be column level or table level. Column level constraints apply to a column, and table level constraints apply to the whole table.
The following constraints are commonly used in SQL:
| Constraint | What it does |
|---|---|
| NOT NULL | Makes sure a column cannot have missing (NULL) values |
| UNIQUE | Makes sure all values in a column are different from each other |
| PRIMARY KEY | Uniquely identifies each row—no duplicates and no NULL values |
| FOREIGN KEY | Connects a column in one table to a column in another table |
| CHECK | Makes sure values meet a certain rule (e.g., numbers must be positive) |
| DEFAULT | Automatically gives a column a value if none is provided |
| INDEX | Makes searching and getting data faster (not a data rule, for performance) |
By applying NOT NULL constraint on a column, you make sure that this column will never have NULL or empty values.
The NOT NULL constraint enforces a column to NOT accept NULL values.
This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
SQL NOT NULL on CREATE TABLE
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);
To add Age column using alter and add NOT NULL CONSTRAINTS
ALTER TABLE Persons
ALTER COLUMN Age int NOT NULL;
The UNIQUE constraint ensures that all values in a column are different.
Both the UNIQUE and PRIMARY KEY constraints provide a guarantee for uniqueness for a column or set of columns. A PRIMARY KEY constraint automatically has a UNIQUE constraint.
However, you can have many UNIQUE constraints per table, but only one PRIMARY KEY constraint per table.
Unique constraints are used to make sure that values inserted into a column across all the rows have unique or distinct values. It can help you to eliminate any duplicate data in a column.
NULL values are allowed in a UNIQUE constraint column. And two NULL values are not same hence multiple rows with NULL values are allowed.
CREATE TABLE Persons (
ID int NOT NULL UNIQUE,
LastName varchar(255) NOT NULL,
FirstName varchar(255),
Age int
);
SQL UNIQUE Constraint on ALTER TABLE
ALTER TABLE Persons
ADD UNIQUE (ID);
ALTER TABLE Persons
ADD CONSTRAINT UC_Person UNIQUE (ID,LastName);
DROP a UNIQUE Constraint
ALTER TABLE Persons
DROP CONSTRAINT UC_Person;