Mastering SQL Concepts

What does SQL stand for?

• Standard Query Language

• Structured Query Language

• Structured Query List

• Simple Query Language

Which SQL command is used to retrieve data from a database?

• UPDATE

• SELECT

• INSERT

• DELETE

What is the purpose of the WHERE clause in SQL?

• To sort records in ascending order.

• To join multiple tables together.

• To filter records based on specified conditions.

• To create new database tables.

Explain the difference between INNER JOIN and LEFT JOIN.

• INNER JOIN fills unmatched rows with default values from the left table.

• INNER JOIN returns all rows from both tables regardless of matches.

• LEFT JOIN only returns rows from the right table with no NULLs.

• INNER JOIN returns matched rows only; LEFT JOIN returns all rows from the left table with matched rows from the right table, filling with NULLs if no match.

What is a primary key in a database?

• A primary key is a type of foreign key.

• A primary key is an optional field in a database.

• A primary key is a unique identifier for a record in a database.

• A primary key can be duplicated across records.

How do you count the number of rows in a SQL table?

• SELECT COUNT(*) FROM table_name;

• COUNT(table_name);

• SELECT SUM(*) FROM table_name;

• SELECT ROW_COUNT(table_name);

What SQL function would you use to find the average value of a column?

• COUNT()

• MAX()

• SUM()

• AVG()

What is a subquery in SQL?

• A subquery is a type of database index.

• A subquery is a nested query within another SQL query.

• A subquery is a command to delete records.

• A subquery is a method for creating tables.

How do you create a view in SQL?

• DROP VIEW view_name;

• CREATE VIEW view_name AS SELECT column1, column2 FROM table_name WHERE condition;

• CREATE TABLE view_name AS SELECT column1, column2 FROM table_name;

• ALTER VIEW view_name SET column1 = value;

What is the purpose of normalization in databases?

• The purpose of normalization is to reduce data redundancy and improve data integrity.

• To eliminate all data from the database completely.

• To simplify database queries and reduce performance.

• To increase data redundancy and decrease data integrity.