SQL Statements

SQL ([[Structured Query Language]]) statements are the means by which users interact with a relational database to perform various operations.

SQL is a domain-specific language used in programming and designed for managing and manipulating data held in a [[relational database management system]] (RDBMS). SQL statements are used to execute tasks such as updating data on a database or retrieving data from a database. There are several types of SQL statements, broadly categorized into the following groups:

1. Data Definition Language (DDL): These statements define the database structure or schema. Some common DDL statements include:
   • CREATE: Used to create a new table or database.
   • ALTER: Used to modify an existing database object, like adding a column to a table.
   • DROP: Used to delete an entire table or database.
   • TRUNCATE: Used to remove all records from a table, including all spaces allocated for the records.
2. Data Manipulation Language (DML): These statements are used for managing data within schema objects. Some common DML statements include:
   • SELECT: Used to retrieve data from a database.
   • INSERT: Used to insert data into a table.
   • UPDATE: Used to update existing data within a table.
   • DELETE: Used to delete records from a database table.
3. Data Control Language (DCL): These statements are used to control access to data in the database. Common DCL statements include:
   • GRANT: Used to give user access privileges to a database.
   • REVOKE: Used to withdraw access privileges given with the GRANT command.
4. Transaction Control Language (TCL): These statements are used to manage the changes made by DML statements. They allow transactions to be grouped together. Common TCL statements include:
   • COMMIT: Used to save the work done.
   • ROLLBACK: Used to undo the work that has not been saved.
   • SAVEPOINT: Used to identify a point in a transaction to which you can later roll back.