SQL Introduction
SQL (Structured Query Language) is a programming language used to manage and manipulate relational databases. It is widely used in many industries, including banking, healthcare, and technology, to manage and analyze data.
SQL is used to perform tasks such as creating databases and tables, inserting, updating, and deleting data, and querying data to retrieve information. SQL has a syntax that is similar to other programming languages, and it uses commands like SELECT, INSERT, UPDATE, DELETE, and JOIN to manipulate data.
SQL can be used with different relational database management systems (RDBMS), such as MySQL, Oracle, Microsoft SQL Server, and PostgreSQL. SQL has become an essential skill for anyone working in data-related fields, and it is a fundamental part of database management and data analysis.
SQL Queries are 4 types of categories
-
- DDL
- DML
- TCL
- DCL
- DDL – Data Definition Language
DDL stands for Data Definition Language, which is a set of SQL commands used to define the structure and layout of a database. It is used to create, modify, and delete the database schema and its objects, such as tables, views, indexes, and constraints.
- Create table
- Alter table
- Rename table
- Drop table
- Truncate table
- Comment
CREATE: This command is used to create a new object, such as a table or view, in the database.
RENAME: This command is used to rename an existing tables or view, in the database.
ALTER: This command is used to modify an existing object in the database, such as changing the column name or data type of a table.
DROP: This command is used to delete an object from the database, such as a table or view.
TRUNCATE: This command is used to delete all data from a table, but keeps the structure of the table intact.
CONSTRAINT: This command is used to define rules for data integrity, such as defining a primary key or foreign key constraint.
DDL statements are executed immediately when they are issued, and they are automatically committed, meaning that changes made using DDL commands cannot be rolled back. Therefore, it is important to be careful when using DDL commands to ensure that they do not have unintended consequences.
- DML – Data Manipulation Language
DML stands for Data Manipulation Language, which is a set of SQL commands used to manipulate the data stored in a database. It is used to insert, update, and delete data from a database, as well as to query data to retrieve information.
- Insert
- Update
- Delete
INSERT: This command is used to add new rows of data into a table.
UPDATE: This command is used to modify existing data in a table.
DELETE: This command is used to remove rows of data from a table.
DML statements are not automatically committed when they are issued, and changes made using DML commands can be rolled back if necessary. Therefore, it is important to use transactions to ensure data integrity and consistency.
DML commands are typically used in conjunction with DDL commands to create and modify the structure of the database, and to manipulate the data stored within it. Together, DDL and DML make up the core components of SQL, and are essential for managing and working with relational databases.
- TCL – Transaction Control Language
TCL stands for Transaction Control Language, which is a set of SQL commands used to manage transactions in a relational database management system. Transactions are used to group one or more SQL statements together into a logical unit of work, so that they can be executed as a single operation.
- Commit
- Rollback
- Savepoint
COMMIT: This command is used to save the changes made by a transaction to the database.
ROLLBACK: This command is used to undo the changes made by a transaction and restore the database to its previous state.
SAVEPOINT: This command is used to create a point in a transaction where the transaction can be rolled back to if necessary.
TCL commands are used to ensure that database transactions are executed in a reliable and consistent manner, and to ensure that the database remains in a valid state at all times. They are typically used in conjunction with DDL and DML commands to create and modify the structure of the database, and to manipulate the data stored within it.
Overall, TCL commands are essential for managing transactions in a database, and are critical for ensuring data integrity and consistency in the face of concurrent access and updates to the database.
- DCL – Data Control Language
DCL stands for Data Control Language, which is a set of SQL commands used to control access to data stored in a relational database management system. DCL commands are used to grant or revoke privileges on database objects, and to define the level of access that users and roles have to those objects.
- Grant
- System
- Object
- Revoke
GRANT: This command is used to give a user or role permission to access and/or modify database objects.
REVOKE: This command is used to remove a user or role's permission to access and/or modify database objects.
DCL commands are essential for managing the security and access control of a database. They ensure that only authorized users and roles are able to access and modify sensitive data, and that the level of access granted to each user or role is appropriate for their needs and responsibilities.
In addition, DCL commands are used to enforce data privacy regulations and compliance requirements, such as HIPAA, GDPR, and PCI-DSS. By controlling access to sensitive data, organizations can ensure that they remain in compliance with these regulations and avoid costly penalties and legal liabilities.
Overall, DCL commands are a critical component of any database management system, and are essential for ensuring data security, privacy, and compliance.