SQL Clauses and Keywords Quiz

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Questions and Answers

What is the purpose of the SELECT statement in SQL?

To add new records to a table

To modify existing records in a table

To remove records from a table

To retrieve data from one or more tables (correct)

Which SQL statement is used to add new records to a table?

INSERT INTO (correct)

DELETE

SELECT

UPDATE

What is the purpose of the UPDATE statement in SQL?

To retrieve data from one or more tables

To modify existing records in a table (correct)

To remove records from a table

To add new records to a table

Which SQL statement is used to remove records from a table?

DELETE FROM Signup and view all the answers

Which of the following is not a key DML command in SQL?

CREATE Signup and view all the answers

What is the main purpose of the Data Manipulation Language (DML) commands in SQL?

To manipulate and interact with the data stored in the database Signup and view all the answers

What clause is used to sort the result set based on specified columns and sorting orders?

ORDER BY Signup and view all the answers

Which keyword ensures that only unique values are returned in a query result?

DISTINCT Signup and view all the answers

What is the purpose of the LIMIT (or FETCH) clause in SQL?

Restricts the number of rows returned in the result set. Signup and view all the answers

What does the SELECT * statement do in SQL?

Retrieves all columns from a table in a database. Signup and view all the answers

Which clause is used to filter groups based on aggregate conditions?

HAVING Signup and view all the answers

In SQL, what does the DISTINCT keyword ensure?

Only unique values are returned. Signup and view all the answers

What does the subquery (SELECT * FROM Books WHERE PublishedYear = 2022 AND Price > 20) do?

Retrieves all columns from the 'Books' table Signup and view all the answers

How can you create a new table based on the result of a subquery in SQL?

By using the CREATE TABLE ... AS statement Signup and view all the answers

What is the purpose of marking a column as 'unused' in SQL?

To remove the column from the table structure Signup and view all the answers

Which command is used to identify the table structure in SQL?

DESCRIBE statement Signup and view all the answers

How can you delete an unused column from a table in SQL?

'DROP COLUMN' command Signup and view all the answers

Which statement permanently removes a column from a table in SQL?

'ALTER TABLE DROP COLUMN' statement Signup and view all the answers

Study Notes

Retrieving Data from a Table

To retrieve all columns from a table, use the SELECT * statement, where * is a wildcard character representing all columns.
Example: SELECT * FROM Books retrieves all columns from the "Books" table.

Creating a New Table with a Subquery

A subquery can be used to create a new table with the CREATE TABLE statement.
Example: CREATE TABLE BestSellers AS (SELECT * FROM Books WHERE PublishedYear = 2022 AND Price > 20) creates a new table "BestSellers" with the same structure as the result of the subquery.

Identifying Table Structure

The DESCRIBE statement can be used to identify the table structure (columns and their data types) in some database systems, such as MySQL or PostgreSQL.
Marking a column as unused can be achieved by renaming the column or creating a new table without the unwanted column.
Deleting an unused column permanently removes the column from the table.

Data Manipulation Language (DML) Commands

DML commands are used for manipulating and interacting with the data stored in a database.
Key DML commands include:
- SELECT: retrieves data from one or more tables.
- INSERT: adds new records to a table.
- UPDATE: modifies existing records in a table.
- DELETE: removes records from a table.

SQL Clauses

GROUP BY clause: groups rows based on specified columns, often used with aggregate functions.
HAVING clause: filters groups based on aggregate conditions.
ORDER BY clause: sorts the result set based on specified columns and sorting orders.
LIMIT (or FETCH) clause: restricts the number of rows returned in the result set.
JOIN clause: combines rows from two or more tables based on related columns.
DISTINCT keyword: ensures that only unique values are returned.

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Description

Test your knowledge on SQL clauses like GROUP BY, HAVING, ORDER BY, LIMIT, JOIN, and keywords like DISTINCT. Learn how to group rows, filter groups, sort results, restrict row count, combine tables, and retrieve unique values in SQL queries.