String quoting and concatenation differences in SQL - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Output of string concatenation with single quotes

What is the output of this SQL query?

SELECT 'Hello' || ' ' || 'World' AS greeting;

SQL

SELECT 'Hello' || ' ' || 'World' AS greeting;

A

greeting
'Hello World'

B

greeting
HelloWorld

C

greeting
Hello World

D SyntaxError

💡 Hint

|| is the string concatenation operator in standard SQL.

The || operator concatenates strings without adding extra characters. The spaces must be included explicitly as strings.

❓ query_result

intermediate

Effect of double quotes on string literals

What error or output does this SQL query produce?

SELECT "Hello" || ' ' || 'World' AS greeting;

SQL

SELECT "Hello" || ' ' || 'World' AS greeting;

A Column "Hello" does not exist

B SyntaxError

C

greeting
NULL

D

greeting
Hello World

💡 Hint

Double quotes in SQL usually denote identifiers, not string literals.

Double quotes are used for column or table names. "Hello" is treated as a column name, which does not exist here.

📝 Syntax

advanced

Correct way to include a single quote inside a string literal

Which SQL query correctly selects the string: It's a sunny day?

Options show different ways to write the string literal.

A SELECT 'It\'s a sunny day' AS sentence;

B SELECT 'It's a sunny day' AS sentence;

C SELECT "It's a sunny day" AS sentence;

D SELECT 'It''s a sunny day' AS sentence;

💡 Hint

In SQL, single quotes inside strings are escaped by doubling them.

Option D doubles the single quote inside the string, which is the correct SQL syntax for including a single quote inside a string literal.

❓ query_result

advanced

Result of concatenating NULL with a string

What is the output of this SQL query?

SELECT 'Hello' || NULL || 'World' AS greeting;

SQL

SELECT 'Hello' || NULL || 'World' AS greeting;

A

greeting
NULL

B

greeting
HelloWorld

C

greeting
Hello World

D SyntaxError

💡 Hint

Concatenating with NULL in SQL usually results in NULL.

In SQL, concatenating any string with NULL results in NULL because NULL represents unknown or missing data.

🧠 Conceptual

expert

Difference between single quotes and double quotes in SQL

Which statement best describes the difference between single quotes and double quotes in standard SQL?

A Single quotes and double quotes can both be used interchangeably for string literals.

B Single quotes are for string literals; double quotes are for identifiers like column or table names.

C Double quotes are used for comments; single quotes are for string literals.

D Single quotes are for numeric values; double quotes are for string literals.

💡 Hint

Think about how SQL treats identifiers and strings differently.

Standard SQL uses single quotes for strings and double quotes for identifiers to allow case sensitivity or special characters in names.