Database Tables in DBMS: DDL Essentials Explained
10 Questions
2 Views

Choose a study mode

Play Quiz
Study Flashcards
Spaced Repetition
Chat to lesson

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What SQL statement is used to remove a column from a table?

  • ALTER TABLE DROP COLUMN (correct)
  • DELETE COLUMN
  • ALTER COLUMN DELETE
  • REMOVE COLUMN

    • How can a table be deleted in SQL?

  • REMOVE customers TABLE;
  • DELETE TABLE customers;
  • DROP TABLE customers; (correct)
  • ALTER TABLE DROP customers;

    • What is the purpose of setting constraints in SQL tables?

  • To enforce data integrity (correct)
  • To change the table structure
  • To improve query performance
  • To apply formatting to table data

    • What does the PRIMARY KEY constraint ensure in a table?

    <p>All values in the column are unique</p> Signup and view all the answers

    When creating tables, what does the FOREIGN KEY constraint establish?

    <p>A relationship between columns in different tables</p> Signup and view all the answers

    What SQL statement is used to create a new table in a Database Management System (DBMS)?

    <p>CREATE TABLE</p> Signup and view all the answers

    In the SQL code snippet provided, what is the data type of the name column in the customers table?

    <p>VARCHAR(50)</p> Signup and view all the answers

    What SQL statement should be used to add a new column named phone to the customers table?

    <p>ADD COLUMN phone VARCHAR(20)</p> Signup and view all the answers

    Which clause in the ALTER TABLE statement is used to modify the properties of an existing column, such as changing the data type or adding constraints?

    <p>ALTER COLUMN</p> Signup and view all the answers

    What does the NOT NULL constraint signify when modifying a table's column in a Database Management System?

    <p>The column cannot contain NULL values</p> Signup and view all the answers

    Study Notes

    Creating, Modifying, and Deleting Tables in a Database Management System (DBMS): DDL Deep Dive

    When building a database to store information, tables are the foundational building blocks. The Database Definition Language (DDL) is a set of instructions used to create, modify, and delete tables in a Database Management System (DBMS). Let's explore these essential DDL concepts in more detail.

    Creating Tables

    To create a table, you use the CREATE TABLE statement, specifying its name, columns, and data types:

    CREATE TABLE customers
(
  id INTEGER PRIMARY KEY,
  name VARCHAR(50) NOT NULL,
  email VARCHAR(100)
);

    This code snippet creates a customers table with three columns: id (an integer primary key), name (a string with a length of 50 characters), and email (a string with a length of 100 characters).

    Modifying Tables

    Sometimes you need to modify existing tables to add or change columns. To do this, you use the ALTER TABLE statement:

    ALTER TABLE customers
ADD COLUMN address VARCHAR(100);

    This statement adds a new column called address (a string with a length of 100 characters) to the customers table.

    To rename a column, you can use the ALTER TABLE statement with the ALTER COLUMN clause:

    ALTER TABLE customers
ALTER COLUMN email VARCHAR(255) NOT NULL;

    This statement changes the data type of the email column to VARCHAR(255) and adds the NOT NULL constraint, which means the column cannot contain null values.

    To delete a column, you use the ALTER TABLE statement with the DROP COLUMN clause:

    ALTER TABLE customers
DROP COLUMN address;

    This statement removes the address column from the customers table.

    Deleting Tables

    When a table is no longer needed, it can be deleted using the DROP TABLE statement:

    DROP TABLE customers;

    This statement removes the customers table from the DBMS.

    Setting Constraints

    Constraints are used to enforce data integrity and ensure the quality of data in a table. Constraints like primary keys, foreign keys, and not null can be declared during table creation or added later using the ALTER TABLE statement:

    CREATE TABLE customers
(
  id INTEGER PRIMARY KEY,
  name VARCHAR(50) NOT NULL,
  email VARCHAR(100) NOT NULL,
  FOREIGN KEY (email) REFERENCES users(email)
);

    This statement creates a customers table with a foreign key constraint on the email column, which references the primary key of another table called users.

    Understanding and applying these DDL concepts are fundamental to building and maintaining a well-structured database. While this article touches upon the basics, DDL can be more complex in reality, and further exploration of advanced features and tools is encouraged.

    Studying That Suits You

    Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

    Quiz Team

    Description

    Learn about creating, modifying, and deleting tables in a Database Management System (DBMS) using the Database Definition Language (DDL). Explore how to set constraints like primary keys and foreign keys for maintaining data integrity. Dive deep into essential DDL concepts for building and managing a well-structured database.

    More Like This

    Use Quizgecko on...
    Browser
    Open
    Browser
    Browser