Practice - 5 Tasks

Answer the questions below

1fill in blank

easy

Complete the code to select common rows from two tables.

SQL

SELECT * FROM employees [1] SELECT * FROM managers;

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

AINTERSECT

BUNION

CEXCEPT

DJOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION instead of INTERSECT returns all rows from both tables.

Using JOIN without ON clause causes syntax error.

✗ Incorrect

The INTERSECT keyword returns only the rows that appear in both queries.

2fill in blank

medium

Complete the code to find common product IDs from two tables.

SQL

SELECT product_id FROM sales_2023 [1] SELECT product_id FROM sales_2024;

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

AUNION ALL

BEXCEPT

CINTERSECT

DLEFT JOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION ALL returns all product IDs, including duplicates.

Using LEFT JOIN returns all from first table, not just common.

✗ Incorrect

INTERSECT returns only product IDs that appear in both sales_2023 and sales_2024.

3fill in blank

hard

Fix the error in the query to get common customer emails from two tables.

SQL

SELECT email FROM customers_2022 [1] SELECT email FROM customers_2023;

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

AUNION

BWHERE

CJOIN

DINTERSECT

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN without ON clause causes syntax error.

Using UNION returns all emails, not just common ones.

✗ Incorrect

To get common emails, use INTERSECT. JOIN and WHERE are incorrect here.

4fill in blank

hard

Fill both blanks to select common employee IDs and order them ascending.

SQL

SELECT employee_id FROM dept_a [1] SELECT employee_id FROM dept_b ORDER BY employee_id [2];

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

AINTERSECT

BDESC

CASC

DUNION

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION returns all IDs, not just common ones.

Using DESC orders in descending order, not ascending.

✗ Incorrect

Use INTERSECT to get common IDs and ASC to order ascending.

5fill in blank

hard

Fill all three blanks to select common product names and prices, filtering price above 100.

SQL

SELECT product_name, price FROM products_2022 [1] SELECT product_name, price FROM products_2023 WHERE price [2] 100 ORDER BY price [3];

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

AINTERSECT

CASC

DUNION

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION returns all products, not just common ones.

Using < instead of > filters wrong prices.

Ordering by DESC sorts prices descending, not ascending.

✗ Incorrect

INTERSECT finds common products, > filters prices above 100, and ASC orders prices ascending.

Practice

(1/5)

1. What does the SQL INTERSECT operator do?

easy

A. Combines rows from both queries including duplicates.

B. Returns all rows from the first SELECT query.

C. Returns all rows from the second SELECT query.

D. Returns only the rows common to both SELECT queries.

Solution

Step 1: Understand the purpose of INTERSECT
The INTERSECT operator compares two SELECT queries and returns only the rows that appear in both results.
Step 2: Compare with other set operators
Unlike UNION or UNION ALL, INTERSECT excludes rows not common to both queries.
Final Answer:
Returns only the rows common to both SELECT queries. -> Option D
Quick Check:
INTERSECT = common rows [OK]

Hint: INTERSECT keeps only shared rows between two queries [OK]

Common Mistakes:

Confusing INTERSECT with UNION which combines all rows
Thinking INTERSECT returns rows from only one query
Assuming INTERSECT includes duplicates

2. Which of the following is the correct syntax to find common rows between two tables TableA and TableB with the same columns id and name?

easy

A. SELECT id, name FROM TableA JOIN TableB ON TableA.id = TableB.id;

B. SELECT id, name FROM TableA UNION SELECT id, name FROM TableB;

C. SELECT id, name FROM TableA INTERSECT SELECT id, name FROM TableB;

D. SELECT id, name FROM TableA WHERE id IN TableB;

Solution

Step 1: Identify correct INTERSECT syntax
The INTERSECT operator is used between two SELECT statements with matching columns and types.
Step 2: Check each option
SELECT id, name FROM TableA INTERSECT SELECT id, name FROM TableB; uses INTERSECT correctly. SELECT id, name FROM TableA UNION SELECT id, name FROM TableB; uses UNION which combines rows. SELECT id, name FROM TableA JOIN TableB ON TableA.id = TableB.id; uses JOIN which is different. SELECT id, name FROM TableA WHERE id IN TableB; has incorrect WHERE syntax.
Final Answer:
SELECT id, name FROM TableA INTERSECT SELECT id, name FROM TableB; -> Option C
Quick Check:
Correct INTERSECT syntax = SELECT id, name FROM TableA INTERSECT SELECT id, name FROM TableB; [OK]

Hint: Use INTERSECT between two SELECTs with matching columns [OK]

Common Mistakes:

Using UNION instead of INTERSECT
Trying to use WHERE with IN incorrectly
Confusing JOIN with INTERSECT

SELECT id, name FROM Employees1 INTERSECT SELECT id, name FROM Employees2;

medium

A. Rows with Bob and Carol only

B. Rows with Alice, Bob, Carol, and Dave

C. Rows with Alice only

D. Rows with Dave only

Solution

Step 1: List rows from both tables
Employees1 has (1, Alice), (2, Bob), (3, Carol). Employees2 has (2, Bob), (3, Carol), (4, Dave).
Step 2: Find common rows
Common rows are those present in both: (2, Bob) and (3, Carol).
Final Answer:
Rows with Bob and Carol only -> Option A
Quick Check:
INTERSECT returns common rows = Bob, Carol [OK]

Hint: INTERSECT returns only rows present in both tables [OK]

Common Mistakes:

Including rows unique to one table
Confusing UNION with INTERSECT
Ignoring column matching in rows

4. Consider this SQL query:

SELECT id, name FROM Customers INTERSECT SELECT id, name FROM Orders;

It returns an error. What is the most likely cause?

medium

A. The columns selected have different data types in Customers and Orders.

B. INTERSECT cannot be used with SELECT statements.

C. The tables Customers and Orders do not exist.

D. INTERSECT requires a WHERE clause.

Solution

Step 1: Understand INTERSECT requirements
INTERSECT requires both SELECT queries to have the same number of columns with compatible data types.
Step 2: Analyze error causes
If columns differ in type (e.g., id is integer in one table and string in another), the query errors. Other options are incorrect because INTERSECT is valid syntax, tables must exist to run, and WHERE is optional.
Final Answer:
The columns selected have different data types in Customers and Orders. -> Option A
Quick Check:
Matching column types required for INTERSECT [OK]

Hint: Check column types match for INTERSECT queries [OK]

Common Mistakes:

Assuming INTERSECT needs WHERE clause
Thinking INTERSECT is invalid syntax
Ignoring data type mismatches

5. You have two tables:
ProductsA with columns product_id, name, price
ProductsB with columns product_id, name, price

You want to find products that exist in both tables with the same product_id and name, ignoring price differences.

Which query correctly uses INTERSECT to achieve this?

hard

A. SELECT product_id, name, price FROM ProductsA INTERSECT SELECT product_id, name, price FROM ProductsB;

B. SELECT product_id, name FROM ProductsA INTERSECT SELECT product_id, name FROM ProductsB;

C. SELECT product_id FROM ProductsA INTERSECT SELECT product_id FROM ProductsB;

D. SELECT * FROM ProductsA INTERSECT SELECT * FROM ProductsB;

Solution

Step 1: Identify columns to compare
You want to compare only product_id and name, ignoring price differences.
Step 2: Use INTERSECT on matching columns
SELECT product_id, name FROM ProductsA INTERSECT SELECT product_id, name FROM ProductsB; selects product_id and name from both tables and intersects them, returning only products common by those two columns.
Step 3: Analyze other options
SELECT product_id, name, price FROM ProductsA INTERSECT SELECT product_id, name, price FROM ProductsB; includes price, so products with different prices won't match. SELECT product_id FROM ProductsA INTERSECT SELECT product_id FROM ProductsB; compares only product_id, ignoring name. SELECT * FROM ProductsA INTERSECT SELECT * FROM ProductsB; compares all columns, including price, which is not desired.
Final Answer:
SELECT product_id, name FROM ProductsA INTERSECT SELECT product_id, name FROM ProductsB; -> Option B
Quick Check:
INTERSECT on selected columns matches desired fields [OK]

Hint: Select only columns to compare before INTERSECT [OK]

Common Mistakes:

Including extra columns that cause mismatches
Selecting * when columns differ
Comparing only one column when two are needed

INTERSECT for common rows in SQL - Interactive Code Practice

Start learning this pattern below

Practice

Solution

Step 1: Understand the purpose of INTERSECT

Step 2: Compare with other set operators

Final Answer:

Quick Check:

Solution

Step 1: Identify correct INTERSECT syntax

Step 2: Check each option

Final Answer:

Quick Check:

Solution

Step 1: List rows from both tables

Step 2: Find common rows

Final Answer:

Quick Check:

Solution

Step 1: Understand INTERSECT requirements

Step 2: Analyze error causes

Final Answer:

Quick Check:

Solution

Step 1: Identify columns to compare

Step 2: Use INTERSECT on matching columns

Step 3: Analyze other options

Final Answer:

Quick Check: