Learn sql Free for beginners

SQL beginners tutorial learn free

SQL Introduction

SQL, or Structured Query Language, is a domain-specific language used in programming and designed for managing and manipulating data within relational database management systems (RDBMS).

It provides a standardized way to interact with databases, enabling users to perform tasks such as querying data, updating data, and managing databases. Here are some key components and concepts related to SQL:

Database Management Systems (DBMS): These are software applications that enable users to interact with databases. Some popular examples include MySQL, PostgreSQL, Microsoft SQL Server, Oracle Database, and SQLite.

Relational Database Management Systems (RDBMS): These are a type of DBMS that organizes data into tables with rows and columns, allowing for the establishment of relationships between different sets of data.

Tables: In SQL, data is organized into tables, which consist of rows and columns. Each column has a specific data type, and each row represents a unique record.

Queries: SQL allows users to retrieve, insert, update, and delete data from a database. Queries are statements that instruct the database to perform these operations.

Data Manipulation Language (DML): This is the subset of SQL used for retrieving and manipulating data. Common DML commands include SELECT, INSERT, UPDATE, and DELETE.

Data Definition Language (DDL): This subset of SQL is used for defining the structure of a database, including creating and modifying database objects such as tables, indexes, and views. Common DDL commands include CREATE, ALTER, and DROP.

Constraints: Constraints are rules that are applied to data columns to ensure the accuracy and reliability of the data in the database. Some common constraints include NOT NULL, UNIQUE, PRIMARY KEY, FOREIGN KEY, and CHECK.

SQL joins

Joins: SQL enables users to combine rows from two or more tables based on a related column between them. Common types of joins include INNER JOIN, LEFT JOIN, RIGHT JOIN, and FULL JOIN.

Functions and Aggregations: SQL provides various built-in functions for performing operations on data, such as mathematical calculations, string manipulations, and date operations.

Aggregation functions, such as SUM, COUNT, AVG, MAX, and MIN, are used to perform calculations on sets of values.

Transactions: SQL supports transactions, which are sequences of database operations that are treated as a single unit. Transactions ensure data integrity and consistency by allowing either all operations to be performed or none at all.

SQL is a powerful tool for managing and querying data in databases, and it is widely used across various industries and applications that rely on data storage and retrieval.

Learning SQL is crucial for anyone working with data or in roles that involve database management and data analysis.

SQL syntax with example

SQL joins

Sure, let me provide you with some basic SQL commands along with examples. Please note that the syntax might vary slightly depending on the specific database management system you are using, but these examples should provide a general understanding.

  1. Creating a Table

CREATE TABLE Persons (

    PersonID int,

    LastName varchar(255),

    FirstName varchar(255),

    Address varchar(255),

    City varchar(255)

);

  1. Inserting Data

INSERT INTO Persons (PersonID, LastName, FirstName, Address, City)

VALUES (1, ‘Doe’, ‘John’, ‘123 Main St’, ‘Anytown’);

  1. Selecting Data

SELECT * FROM Persons;

  1. Updating Data

UPDATE Persons

SET City = ‘Newtown’

WHERE PersonID = 1;

  1. Deleting Data

DELETE FROM Persons

WHERE PersonID = 1;

  1. Creating a Primary Key

CREATE TABLE Persons (

    PersonID int NOT NULL PRIMARY KEY,

    LastName varchar(255),

    FirstName varchar(255),

    Address varchar(255),

    City varchar(255)

);

  1. Using Constraints

CREATE TABLE Orders (

    OrderID int NOT NULL PRIMARY KEY,

    OrderNumber int NOT NULL,

    PersonID int,

    CONSTRAINT FK_PersonOrder FOREIGN KEY (PersonID)

    REFERENCES Persons(PersonID)

);

  1. Using Joins

SELECT Persons.LastName, Persons.FirstName, Orders.OrderNumber

FROM Persons

INNER JOIN Orders

ON Persons.PersonID = Orders.PersonID;

  1. Using Aggregate Functions

SELECT COUNT(*) AS OrderCount

FROM Orders;

  1. Creating Views

CREATE VIEW [YoungPersons] AS

SELECT * FROM Persons

WHERE Age < 30;

These examples provide a basic understanding of some common SQL commands. Keep in mind that SQL syntax may vary depending on the specific database system you are using

SQL select

The SELECT statement is one of the most fundamental SQL commands, used to retrieve data from a database. It allows you to specify the columns you want to retrieve as well as any conditions to filter the rows. The basic syntax of a SELECT statement is as follows:

SELECT column1, column2, …

FROM table_name

WHERE condition;

Here’s a brief explanation of each part:

SELECT: This keyword specifies the columns that you want to retrieve. You can use an asterisk (*) to select all columns.

FROM: This keyword specifies the table from which you want to retrieve the data.

WHERE: This optional keyword allows you to specify conditions that must be met for the rows to be selected. If omitted, all rows will be selected.

Here are some examples of using the SELECT statement:

  1. Selecting All Columns

SELECT * FROM Customers;

  1. Selecting Specific Columns

SELECT CustomerName, City, Country FROM Customers;

  1. Using WHERE to Filter Rows

SELECT * FROM Customers

WHERE Country = ‘Germany’;

  1. Using Logical Operators with WHERE

SELECT * FROM Customers

WHERE Country = ‘Germany’ AND City = ‘Berlin’;

  1. Using LIKE for Pattern Matching

SELECT * FROM Customers

WHERE ContactName LIKE ‘M%’;

  1. Using ORDER BY to Sort Results

SELECT * FROM Customers

ORDER BY Country;

  1. Using DISTINCT to Retrieve Unique Rows

SELECT DISTINCT Country FROM Customers;

  1. Using LIMIT to Control Result Set Size

SELECT * FROM Customers

LIMIT 5;

These are some common examples of using the SELECT statement in SQL. Depending on the specific database management system you are using, there might be some differences in syntax and additional functionalities.

SQL Select Distinct

The SELECT DISTINCT statement is used to retrieve unique values from a specified column in a table. It filters out duplicate records and returns only distinct (different) values. The basic syntax for using

SELECT DISTINCT is as follows:

SELECT DISTINCT column1, column2, …

FROM table_name;

SELECT DISTINCT: This keyword combination is used to retrieve unique values from the specified columns.

column1, column2, …: These are the names of the columns from which you want to retrieve distinct values.

table_name: This is the name of the table from which you are selecting the distinct values.

Here are some examples of using the SELECT DISTINCT statement:

  1. Selecting Distinct Values from a Single Column

SELECT DISTINCT column_name

FROM table_name;

  1. Selecting Distinct Values from Multiple Columns

SELECT DISTINCT column1, column2

FROM table_name;

  1. Example with a Specific Table

Suppose you have a table called “Products” with columns “ProductID” and “ProductName,” and you want to retrieve the distinct product names. The SQL query would be:

SELECT DISTINCT ProductName

FROM Products;

  1. Using SELECT DISTINCT with Conditions

You can also use SELECT DISTINCT in conjunction with other SQL clauses like WHERE to further filter the results. For example:

SELECT DISTINCT column_name

FROM table_name

WHERE condition;

This query will return distinct values from the specified column that satisfy the given condition.

Using the SELECT DISTINCT statement is helpful when you want to identify unique values within a specific column or combination of columns in your database.

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