What is PostgreSQL - Interactive Quiz & Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all columns from a table named users.

PostgreSQL

SELECT [1] FROM users;

Drag options to blanks, or click blank then click option'

A*

BALL

CCOLUMNS

DEVERYTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'ALL' instead of '*' causes syntax error.

Writing 'COLUMNS' or 'EVERYTHING' is not valid SQL.

The asterisk (*) means select all columns from the table.

2fill in blank

medium

Complete the code to create a new table named products with an id column.

PostgreSQL

CREATE TABLE [1] (id SERIAL PRIMARY KEY);

Drag options to blanks, or click blank then click option'

Aorders

Bproducts

Citems

Dcustomers

Attempts:

3 left

💡 Hint

Common Mistakes

Using wrong table names like 'items' or 'orders'.

Misspelling the table name.

The table name should be 'products' as requested.

3fill in blank

hard

Fix the error in the query to get the count of rows in the users table.

PostgreSQL

SELECT COUNT([1]) FROM users;

Drag options to blanks, or click blank then click option'

Auser_id

Bid

Call

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column name that may have nulls, causing wrong counts.

Using 'all' which is not valid syntax.

Using COUNT(*) counts all rows regardless of column values.

4fill in blank

hard

Fill all three blanks to select name and age from people where age is greater than 30.

PostgreSQL

SELECT [1], [2] FROM people WHERE age [3] 30;

Drag options to blanks, or click blank then click option'

Aname

Bage

C>

D<

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' instead of '>' in the WHERE clause.

Selecting wrong columns or missing commas.

Select 'name' and 'age' columns and filter rows where age is greater than 30.

5fill in blank

hard

Fill all three blanks to insert a new user with name 'Alice' and age 25 into the users table.

PostgreSQL

INSERT INTO users ([1], [2]) VALUES ([3], 25);

Drag options to blanks, or click blank then click option'

Aname

B'Alice'

Cage

D'25'

Attempts:

3 left

💡 Hint

Common Mistakes

Putting numeric values in quotes.

Mixing up column names and values.

Insert into columns 'name' and 'age' the values 'Alice' and 25 respectively.

Practice

1. What is PostgreSQL primarily used for?

easy

A. Creating graphics

B. Designing websites

C. Storing and managing data using tables

D. Writing mobile apps

Solution

1. Step 1: Understand PostgreSQL's purpose

   PostgreSQL is a database system designed to store and manage data.

2. Step 2: Compare options with PostgreSQL's use

   Only storing and managing data using tables matches PostgreSQL's function.

3. Final Answer:

   Storing and managing data using tables -> Option C

4. Quick Check:

   PostgreSQL = Data storage and management [OK]

Hint: PostgreSQL is a database, not a design or app tool [OK]

Common Mistakes:

• Confusing PostgreSQL with web design tools
• Thinking PostgreSQL creates graphics
• Assuming PostgreSQL is for mobile apps

2. Which of the following is the correct way to start a SQL query in PostgreSQL?

easy

A. GET * FROM table_name;

B. SELECT * FROM table_name;

C. FIND * IN table_name;

D. SHOW ALL FROM table_name;

Solution

1. Step 1: Recall SQL syntax for retrieving data

   The standard SQL command to get all data from a table is SELECT * FROM table_name;

2. Step 2: Check each option's validity

   Only SELECT * FROM table_name; uses correct SQL syntax; others are invalid commands.

3. Final Answer:

   SELECT * FROM table_name; -> Option B

4. Quick Check:

   Correct SQL SELECT syntax = SELECT * FROM table_name; [OK]

Hint: SQL queries start with SELECT to get data [OK]

Common Mistakes:

• Using GET instead of SELECT
• Using FIND or SHOW incorrectly
• Missing semicolon at end

3. What will be the result of this query in PostgreSQL?

CREATE TABLE fruits (id INT, name TEXT);
INSERT INTO fruits VALUES (1, 'Apple'), (2, 'Banana');
SELECT name FROM fruits WHERE id = 2;

medium

A. Banana

B. Apple

C. 1

D. No rows returned

Solution

1. Step 1: Understand the table and inserted data

   The table 'fruits' has two rows: (1, 'Apple') and (2, 'Banana').

2. Step 2: Analyze the SELECT query condition

   The query selects 'name' where id = 2, which matches 'Banana'.

3. Final Answer:

   Banana -> Option A

4. Quick Check:

   id=2 corresponds to Banana [OK]

Hint: Match WHERE condition to row values to find output [OK]

Common Mistakes:

• Confusing id with name
• Expecting multiple rows
• Thinking query returns id instead of name

4. Identify the error in this PostgreSQL query:

INSERT INTO users (id, name VALUES (1, 'John');

medium

A. Missing quotes around 'John'

B. Wrong table name

C. Using INSERT instead of UPDATE

D. Missing closing parenthesis after column names

Solution

1. Step 1: Check syntax of INSERT statement

   The column list must be enclosed in parentheses: (id, name)

2. Step 2: Identify missing parenthesis

   The query misses the closing parenthesis after 'name', causing syntax error.

3. Final Answer:

   Missing closing parenthesis after column names -> Option D

4. Quick Check:

   Parentheses must enclose columns list [OK]

Hint: Count parentheses carefully in SQL statements [OK]

Common Mistakes:

• Forgetting closing parenthesis
• Misplacing quotes
• Confusing INSERT with UPDATE

5. You want to store user information with unique IDs and names in PostgreSQL. Which feature ensures IDs are unique and automatically assigned?

hard

A. PRIMARY KEY with SERIAL type

B. TEXT column with UNIQUE constraint

C. FOREIGN KEY referencing another table

D. CHECK constraint on name length

Solution

1. Step 1: Understand uniqueness and auto-assignment

   Unique IDs that auto-increment are done using PRIMARY KEY with SERIAL type in PostgreSQL.

2. Step 2: Evaluate other options

   TEXT with UNIQUE only ensures uniqueness but no auto-assignment; FOREIGN KEY links tables; CHECK validates data but doesn't assign IDs.

3. Final Answer:

   PRIMARY KEY with SERIAL type -> Option A

4. Quick Check:

   Auto-increment unique IDs = PRIMARY KEY + SERIAL [OK]

Hint: Use SERIAL type with PRIMARY KEY for auto IDs [OK]

Common Mistakes:

• Using UNIQUE without auto-increment
• Confusing FOREIGN KEY with unique ID
• Using CHECK for uniqueness