SQL as the query language in Intro to Computing - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the SQL query to select all columns from the table named 'employees'.

Intro to Computing

SELECT [1] FROM employees;

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

AALL

BCOLUMNS

C*

DEVERYTHING

Attempts:

3 left

💡 Hint

Common Mistakes

Using words like ALL or COLUMNS instead of *

Forgetting to specify columns or *

In SQL, * means select all columns from the table.

2fill in blank

medium

Complete the SQL query to select the 'name' column from the 'students' table where the 'age' is greater than 18.

Intro to Computing

SELECT name FROM students WHERE age [1] 18;

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

A=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using = instead of >

Using < which means less than

The symbol > means 'greater than' in SQL, so it selects students older than 18.

3fill in blank

hard

Fix the error in the SQL query to count the number of rows in the 'orders' table.

Intro to Computing

SELECT COUNT([1]) FROM orders;

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

A*

Border_id

Call

Drows

Attempts:

3 left

💡 Hint

Common Mistakes

Using a column name instead of *

Using invalid keywords like 'all' or 'rows'

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

4fill in blank

hard

Fill all blanks to select the 'product' and 'price' columns from 'inventory' where 'price' is less than 100.

Intro to Computing

SELECT [1], [2] FROM inventory WHERE price [3] 100;

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

Aproduct

Bprice

C<

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping column names

Using > instead of < for price condition

Select the columns product and price, and use < to filter prices less than 100.

5fill in blank

hard

Fill all three blanks to create a dictionary-like result with keys as uppercase 'category' and values as 'count' of items where count is greater than 10.

Intro to Computing

SELECT [1] AS category_upper, [2] FROM products WHERE [3] > 10;

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

AUPPER(category)

Bcount

Dcategory

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'category' instead of 'count' for the filter

Not using UPPER() for uppercase

Use UPPER(category) to get uppercase category names, select count column, and filter where count is greater than 10.

Practice

1. What does the SELECT statement do in SQL?

easy

A. It deletes rows from a table.

B. It chooses which columns to show from a table.

C. It creates a new table in the database.

D. It updates values in a table.

Solution

1. Step 1: Understand the purpose of SELECT

   The SELECT statement is used to specify which columns of data you want to see from a table.

2. Step 2: Differentiate from other SQL commands

   Commands like DELETE, CREATE, and UPDATE perform different actions such as removing, creating, or changing data, not selecting columns.

3. Final Answer:

   It chooses which columns to show from a table. -> Option B

4. Quick Check:

   SELECT = choose columns [OK]

Hint: SELECT picks columns to display, not rows or tables [OK]

Common Mistakes:

• Confusing SELECT with DELETE or UPDATE
• Thinking SELECT creates or deletes tables
• Mixing SELECT with WHERE filtering

2. Which of the following is the correct syntax to select the column name from a table called students?

easy

A. SELECT name FROM students;

B. SELECT FROM students name;

C. FROM students SELECT name;

D. SELECT name students FROM;

Solution

1. Step 1: Recall SQL SELECT syntax

   The correct order is SELECT [columns] FROM [table]; so the column name comes after SELECT and the table name after FROM.

2. Step 2: Check each option

   SELECT name FROM students; follows the correct syntax. The other options have incorrect order or missing keywords.

3. Final Answer:

   SELECT name FROM students; -> Option A

4. Quick Check:

   SELECT column FROM table [OK]

Hint: Remember: SELECT columns FROM table; [OK]

Common Mistakes:

• Swapping SELECT and FROM keywords
• Omitting semicolon at the end
• Placing table name before SELECT

3. Given the table employees with columns id, name, and salary, what will this query return?

SELECT name FROM employees WHERE salary > 50000;

medium

A. An error because salary comparison is invalid.

B. All employee names with salary less than 50000.

C. All employee names regardless of salary.

D. All employee names with salary greater than 50000.

Solution

1. Step 1: Understand the WHERE clause

   The WHERE clause filters rows to only those where the salary is greater than 50000.

2. Step 2: Identify the selected column

   The query selects only the name column from the filtered rows.

3. Final Answer:

   All employee names with salary greater than 50000. -> Option D

4. Quick Check:

   WHERE salary > 50000 filters rows [OK]

Hint: WHERE filters rows; SELECT chooses columns [OK]

Common Mistakes:

• Confusing > with < in WHERE clause
• Thinking all columns are returned
• Assuming syntax error due to comparison

4. Identify the error in this SQL query:

SELECT name salary FROM employees;

medium

A. Missing comma between column names.

B. Table name is incorrect.

C. SELECT keyword is misspelled.

D. WHERE clause is missing.

Solution

1. Step 1: Check column list syntax

   When selecting multiple columns, they must be separated by commas. Here, name salary lacks a comma.

2. Step 2: Verify other parts

   The table name employees is correct, SELECT is spelled correctly, and WHERE is optional.

3. Final Answer:

   Missing comma between column names. -> Option A

4. Quick Check:

   Multiple columns need commas [OK]

Hint: Separate columns with commas in SELECT [OK]

Common Mistakes:

• Omitting commas between columns
• Adding unnecessary WHERE clause
• Misspelling keywords

5. You have a table products with columns product_id, name, and price. You want to find all products priced between 10 and 20 inclusive. Which query correctly does this?

hard

A. SELECT name FROM products WHERE price >= 10 OR price <= 20;

B. SELECT name FROM products WHERE price > 10 OR price < 20;

C. SELECT name FROM products WHERE price BETWEEN 10 AND 20;

D. SELECT name FROM products WHERE price = 10 AND price = 20;

Solution

1. Step 1: Understand the BETWEEN operator

   BETWEEN checks if a value is within a range inclusive of the boundaries, so price BETWEEN 10 AND 20 means price ≥ 10 and ≤ 20.

2. Step 2: Compare other options

   SELECT name FROM products WHERE price >= 10 OR price <= 20; uses OR which selects nearly all products; SELECT name FROM products WHERE price > 10 OR price < 20; uses OR which includes prices outside the range; SELECT name FROM products WHERE price = 10 AND price = 20; checks impossible condition price = 10 AND price = 20 simultaneously.

3. Final Answer:

   SELECT name FROM products WHERE price BETWEEN 10 AND 20; -> Option C

4. Quick Check:

   BETWEEN includes range boundaries [OK]

Hint: Use BETWEEN for inclusive range filtering [OK]

Common Mistakes:

• Using OR instead of AND for range
• Confusing BETWEEN with equality
• Checking impossible conditions with AND