A Beginner's Guide to Understanding the Subsets of SQL

SQL (Structured Query Language) is a programming language used to manage and manipulate data stored in a relational database. SQL queries are used to retrieve, insert, update and delete data from the database. SQL queries are divided into four main categories based on their functionality. In this blog, we'll explore the subsets of SQL.

1. Data Definition Language (DDL):

DDL queries are used to define and modify the structure of a database. The following SQL commands are used for DDL:

• CREATE: Creates a database, table, schema, index or any other object in the database.
• DROP: Drops tables, views, procedures, indexes and other database objects.
• ALTER: Alters the definition of database objects like tables, views, procedures, and indexes.
• TRUNCATE: Removes all data from a table.
• ADD COLUMN: Adds a column to an existing table.
• RENAME: Renames a table or a column.

2. Data Manipulation Language (DML):

DML queries are used to manipulate data in a database. The following SQL commands are used for DML:

• SELECT: Retrieves data from one or more tables.
• INSERT: Inserts data or records into a table.
• UPDATE: Updates the values of records in a table.
• DELETE: Deletes records from a table.
• MERGE: Combines data from two or more tables.

3. Data Control Language (DCL):

DCL queries manage the access rights and permission control of the database. The following SQL commands are used for DCL:

• GRANT: Grants access rights to a user or a group of users for a specific object in the database.
• REVOKE: Withdraws permission from users or groups of users for a specific object in the database.

4. Transaction Control Language (TCL):

TCL queries manage transactions in a database. The following SQL commands are used for TCL:

• COMMIT: Makes the changes made in a transaction permanent.
• ROLLBACK: Undoes the changes made in a transaction and restores the database to its previous state.
• SAVEPOINT: Creates a savepoint in a transaction that can be rolled back to.
• SET TRANSACTION: Sets the characteristics of a transaction.

In conclusion, SQL queries are divided into four subsets based on their functionality: Data Definition Language (DDL), Data Manipulation Language (DML), Data Control Language (DCL), and Transaction Control Language (TCL). DDL queries define and modify the structure of a database, DML queries manipulate data in a database, DCL queries manage access rights and permission control, and TCL queries manage transactions in a database. Understanding these subsets is crucial for effective database management using SQL.