📗 SQL
SQL stands for Structured Query Language. It is a programming language that is used for managing and manipulating relational databases. SQL allows users to insert, update, delete, and retrieve data from a database. It is widely used in the field of database management and is an essential tool for anyone working with data. SQL is used by database administrators, data analysts, data scientists, software developers, and other professionals who work with data on a regular basis.
✔ Why SQL is important?
SQL (Structured Query Language) is important for several reasons:
It is the standard language used for managing and manipulating data in relational databases. This means that it is a common language used by database administrators, developers, and analysts to interact with data.
SQL provides a powerful set of tools for querying, sorting, and filtering data in databases. This allows users to extract the information they need quickly and easily, without having to manually sort through large amounts of data.
SQL is used for creating, modifying, and deleting database objects, such as tables, indexes, and views. This provides a way to organize and structure data in a logical and efficient manner.
SQL supports complex operations and calculations on large datasets, making it an essential tool for data analysis and business intelligence.
SQL is used across a wide range of industries and applications, from financial services and healthcare to social media and e-commerce. This means that knowledge of SQL is in high demand, making it a valuable skill for professionals in many fields.
📗 Types of SQL commands
SQL (Structured Query Language) commands are used to manage and manipulate data in a database. There are several types of SQL commands, each designed for a specific purpose. Here are the most common types of SQL commands with examples:
♦ Data Definition Language (DDL) Commands
DDL commands are used to define and manage the structure of database objects such as tables, indexes, views, and constraints. The most common DDL commands are:
CREATE: Used to create new database objects such as tables, views, indexes, etc. Example:
CREATE TABLE customers (
id INT PRIMARY KEY,
name VARCHAR(50),
email VARCHAR(50)
);
ALTER: Used to modify the structure of existing database objects. Example:
ALTER TABLE customers ADD address VARCHAR(100);
DROP: Used to delete database objects such as tables, views, indexes, etc. Example:
DROP TABLE customers;
♦ Data Manipulation Language (DML) Commands
DML commands are used to manipulate data in the database objects. The most common DML commands are:
SELECT: Used to retrieve data from one or more tables in a database. Example:
SELECT * FROM customers WHERE name = 'John';
INSERT: Used to insert new data into a table. Example:
INSERT INTO customers (id, name, email) VALUES (1, 'John', 'john@example.com');
UPDATE: Used to modify existing data in a table. Example:
UPDATE customers SET email = 'john.doe@example.com' WHERE id = 1;
DELETE: Used to delete data from a table. Example:
DELETE FROM customers WHERE id = 1;
♦ Data Control Language (DCL) Commands
DCL commands are used to control access to the database and its objects. The most common DCL commands are:
GRANT: Used to grant specific privileges to a user or a role. Example:
GRANT SELECT, INSERT ON customers TO user1;
REVOKE: Used to revoke specific privileges from a user or a role. Example:
REVOKE SELECT ON customers FROM user1;
♦ Transaction Control Commands
Transaction control commands are used to manage transactions in the database. The most common transaction control commands are:
COMMIT: Used to save changes made in a transaction. Example:
COMMIT;
ROLLBACK: Used to undo changes made in a transaction. Example:
ROLLBACK;
TCL commands are used to manage transactions, which are a group of SQL statements that are executed as a single unit of work. Here are some examples of TCL commands:
COMMIT;
ROLLBACK;
SAVEPOINT savepoint_name;
ROLLBACK TO savepoint_name;
♦ Data Query Language (DQL) Commands
DQL stands for Data Query Language, which is a subset of SQL (Structured Query Language) used to retrieve data from a database. It is specifically designed to query and retrieve data from one or more tables in a database.
The most common DQL command is the SELECT statement, which is used to retrieve data from one or more tables. The basic syntax of the SELECT statement is:
SELECT column1, column2, ... FROM table_name WHERE condition;
Where column1, column2, ... are the columns to retrieve data from, table_name is the name of the table, and condition is an optional condition to filter the data.
In addition to the SELECT statement, DQL also includes other commands such as:
DISTINCT: This command is used to retrieve distinct values of a column from a table.
SELECT DISTINCT column_name FROM table_name;
GROUP BY: This command is used to group rows in a table based on one or more columns.
SELECT column1, COUNT(column2) FROM table_name GROUP BY column1;
HAVING: This command is used to filter data based on a group of rows created by the GROUP BY command.
SELECT column1, COUNT(column2) FROM table_name GROUP BY column1 HAVING COUNT(column2) > 1;
Overall, SQL commands are used to manage and manipulate data in a database. Understanding the different types of SQL commands and their usage is essential for working with databases effectively.
📗 DDL vs DCL vs DML
Here is a tabular comparison of DDL (Data Definition Language), DML (Data Manipulation Language), and DCL (Data Control Language) commands:
In summary, DDL commands are used to create and modify the structure of a database, DML commands are used to manipulate data within a database, and DCL commands are used to control access to database objects. By understanding these different types of SQL commands, you can effectively manage and manipulate data in a database.
Thanks for reading, and happy coding!
Mastering SQL: Essential Commands for Database Management -> Mastering DBMS Joins: Joining Tables in a Database Management System