Introduction to SQL - What is SQL ?

Introduction to SQL

SQL, which stands for Structured Query Language, is a programming language designed for managing and manipulating relational databases. It provides a standardized way to interact with databases and perform various operations on the data.

SQL allows you to:

• Retrieve data using queries
• Insert, update, or delete records
• Create and modify database structures
• Manage database users and permissions
• Perform complex calculations and data transformations

SQL is widely used in web development, data analysis, and other fields where working with relational databases is essential.

Retrieving Data with SQL SELECT

The SELECT statement is used in SQL to retrieve data from a database table. It allows you to specify the columns you want to fetch and apply conditions to filter the results.

Here's an example:

SELECT column1, column2 FROM tablename WHERE condition;

This query selects specific columns (column1, column2) from the table tablename based on a condition defined in the WHERE clause. The result will be a set of rows that meet the specified criteria.

Inserting Data with SQL INSERT

The INSERT statement in SQL is used to add new records to a database table. It allows you to specify the values to be inserted into specific columns or insert data from another table.

Here's an example:

INSERT INTO tablename (column1, column2) VALUES (value1, value2);

This query inserts values (value1, value2) into specified columns (column1, column2) of the table tablename. The data will be added as a new record in the table.

Updating Data with SQL UPDATE

The UPDATE statement in SQL is used to modify existing records in a database table. It allows you to update specific columns with new values based on specified conditions.

Here's an example:

UPDATE tablename SET column1 = newvalue WHERE condition;

This query updates the value of column1 to newvalue in the table tablename for the records that satisfy the specified condition defined in the WHERE clause.

Deleting Data with SQL DELETE

The DELETE statement in SQL is used to remove records from a database table. It allows you to specify conditions to delete specific rows or delete all rows from the table.

Here's an example:

DELETE FROM tablename WHERE condition;

This query deletes rows from the table tablename that satisfy the specified condition defined in the WHERE clause. If no condition is provided, all rows from the table will be deleted.

Creating Tables with SQL CREATE

The CREATE statement in SQL is used to create a new database table. It allows you to define the table's structure by specifying column names, data types, and other constraints.

Here's an example:

CREATE TABLE tablename (
    column1 datatype constraint,
    column2 datatype constraint,
    ...
  );

This query creates a new table named tablename with specified columns, data types, and constraints. You can define primary keys, foreign keys, uniqueness constraints, and other rules as needed.