Introduction

Question 1

SQL, which stands for Structured Query Language, is a programming language that is used to communicate with and manage databases.

Question 2

Data Definition Language (DDL)

Answer 2

It lets you to create, alter, or delete databases and their related objects like tables, views, etc. Commands include CREATE, ALTER, DROP, and TRUNCATE.

Question 3

Data Manipulation Language (DML)

Answer 3

It lets you manage data within database objects. These commands include SELECT, INSERT, UPDATE, and DELETE.

Question 4

Data Control Language (DCL)

Answer 4

It includes commands like GRANT and REVOKE, which primarily deal with rights, permissions and other control-level management tasks for the database system.

Question 5

What’s a database?

Answer 5

A database is an organized collection of data.

Question 6

The SELECT first_name, FROM employees, and WHERE are clauses in the SQL statement. Some clauses are mandatory e.g., the SELECT and FROM clauses whereas others are optional such as the WHERE clause.

Question 7

Each command is composed of tokens that can be literals, keywords, identifiers, or expressions. Tokens are separated by space, tabs, or newlines.

Question 8

Literals

Answer 8

Literals are explicit values which are also known as constants. SQL provides three kinds of literals: string, numeric, and binary.

Question 9

String literal consists of one or more alphanumeric characters surrounded by single quotes

Question 10

50 is a number. However, if you surround it with single quotes e.g., ‘50’, SQL treats it as a string literal.

Question 11

SQL is case sensitive with respect to string literals, so the value ‘John’ is not the same as ‘JOHN’

Question 12

Numeric literals are the integer, decimal, or scientific notation, for example:

200
-5
6.0221415E23

Question 13

SQL represents binary value using the notation x’0000’, where each digit is hexadecimal value

Question 14

Keywords

Answer 14

SQL has many keywords that have special meanings such as SELECT, INSERT, UPDATE, DELETE, and DROP. These keywords are the reserved words, therefore, you cannot use them as the name of tables, columns, indexes, views, stored procedures, triggers, or other database objects.

Question 15

Identifiers

Answer 15

Identifiers refer to specific objects in the database such as tables, columns, indexes, etc. SQL is case-insensitive with respect to keywords and identifiers.

Question 16

When parsing SQL statements with comments, the database engine ignores the characters in the comments.

A comment is denoted by two consecutive hyphens ( –) that allow you to comment the remaining line.
– employees with low salary

Question 17

To document the code that can span multiple lines, you use the multiline C-style notation ( /**/)
/* increase 5% for employees whose salary is less than 3,000 */