SQL language is used to manage and manipulate data stored in relational databases. SQL statements are commands that are used to interact with a database, and they can be used to perform a wide range of tasks, from querying and updating data to creating and deleting tables.
There are different types of SQL statements that perform various operations on a database. In this response, we will discuss some of the most commonly used SQL statements, including DDL, DML, and TCL.
DDL (Data Definition Language) Statements
DDL statements are used to create, modify, and delete database objects such as tables, views, indexes, and constraints. Some of the commonly used DDL statements are:
CREATE statement is used to create a new database object like a table, view, or index. The CREATE TABLE statement is used to create a new table in a database. It specifies the table name, the columns that the table will have, and any constraints or indexes that should be applied to the table.
ALTER statement is used to modify an existing database object such as adding or dropping columns, renaming tables, or modifying constraints. The ALTER TABLE statement is used to modify the structure of an existing table in a database. It can be used to add or remove columns, change column data types, or modify table constraints.
DROP statement is used to delete an existing database object. The DROP TABLE statement is used to delete an existing table or database in a database. It permanently removes the table or database and all of its data.
DML (Data Manipulation Language) Statements
DML statements are used to manipulate the data stored in the database objects. Some of the commonly used DML statements are:
SELECT statement is used to retrieve data from one or more tables in a database. It is used to specify the columns and tables that you want to retrieve data from and can be used with various clauses such as WHERE, GROUP BY, and ORDER BY to filter and sort the data.
INSERT statement is used to add new data to a table in a database. It specifies the table and the values that you want to insert into the table.
UPDATE statement is used to modify existing data in a table in a database. It specifies the table, the columns that you want to modify, and the new values that you want to set.
DELETE statement is used to remove data from a table in a database. It specifies the table and the conditions that must be met for the data to be deleted.
TCL (Transaction Control Language) Statements
TCL statements are used to manage transactions in a database. Transactions are a set of database operations that need to be performed as a single unit of work. Some of the commonly used TCL statements are:
COMMIT statement is used to save the changes made to the database during a transaction.
ROLLBACK statement is used to undo the changes made to the database during a transaction.
SQL statements are essential for working with relational databases, and they can be used to perform a wide range of tasks. By understanding the different types of SQL statements and how to use them, you can effectively manage and manipulate data in a database.