Non-equi joins in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to join two tables where the employee's salary is greater than the department's budget.

SQL

SELECT e.name, d.department_name FROM employees e JOIN departments d ON e.salary [1] d.budget;

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

A=

B<

C>

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' instead of '>' causes the join to only match equal salaries and budgets.

Using '<' or '<=' will join rows where salary is less than or equal to budget, which is not what we want.

The query joins employees and departments where the employee's salary is greater than the department's budget, so the operator should be >.

2fill in blank

medium

Complete the code to join orders and shipments where the shipment date is on or after the order date.

SQL

SELECT o.order_id, s.shipment_date FROM orders o JOIN shipments s ON s.shipment_date [1] o.order_date;

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

A>=

B<

C=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '=' only matches shipment dates exactly equal to order dates.

Using '<' or '<=' would match shipment dates before order dates, which is incorrect.

The join condition requires shipment dates to be on or after order dates, so the operator should be >=.

3fill in blank

hard

Fix the error in the join condition to correctly join products and discounts where the discount start date is before the product release date.

SQL

SELECT p.product_name, d.discount_rate FROM products p JOIN discounts d ON d.start_date [1] p.release_date;

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

A<

B>

C>=

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '>=' would mean the discount starts after or on the release date, which is wrong.

Using '=' only matches exact dates, missing other valid rows.

The discount start date should be before the product release date, so the operator should be <.

4fill in blank

hard

Fill both blanks to join employees and projects where the employee's experience is between the project's minimum and maximum experience requirements.

SQL

SELECT e.name, p.project_name FROM employees e JOIN projects p ON e.experience [1] p.min_experience AND e.experience [2] p.max_experience;

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

A>=

B<

C<=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using < or > incorrectly reverses the range logic.

Using '=' only matches exact experience values, missing others.

The employee's experience should be greater than or equal to the minimum and less than or equal to the maximum experience required by the project.

5fill in blank

hard

Fill all three blanks to join sales and targets where the sale amount is greater than the target minimum, less than the target maximum, and the sale date is on or after the target start date.

SQL

SELECT s.sale_id, t.target_name FROM sales s JOIN targets t ON s.amount [1] t.min_amount AND s.amount [2] t.max_amount AND s.sale_date [3] t.start_date;

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

A>

B<

C>=

D<=

Attempts:

3 left

💡 Hint

Common Mistakes

Using <= or >= incorrectly for amount comparisons.

Using < or > for date comparison misses the 'on or after' condition.

The sale amount should be greater than the minimum and less than the maximum target amounts, and the sale date should be on or after the target start date.

Practice

1. What is a non-equi join in SQL?

easy

A. A join that uses conditions other than equality, like <, >, or BETWEEN.

B. A join that only matches rows with equal values in both tables.

C. A join that combines all rows from both tables regardless of condition.

D. A join that uses only the AND logical operator in the ON clause.

Solution

1. Step 1: Understand join conditions

   Equi joins use equality (=) to match rows. Non-equi joins use other operators like <, >, or BETWEEN.

2. Step 2: Identify non-equi join definition

   Since non-equi joins match rows based on inequalities or ranges, A join that uses conditions other than equality, like <, >, or BETWEEN. correctly describes this.

3. Final Answer:

   A join that uses conditions other than equality, like <, >, or BETWEEN. -> Option A

4. Quick Check:

   Non-equi join = condition other than = [OK]

Hint: Non-equi joins use <, >, or BETWEEN, not just = [OK]

Common Mistakes:

• Confusing non-equi join with equi join
• Thinking non-equi join matches all rows
• Assuming only AND operator defines non-equi join

2. Which of the following is the correct syntax for a non-equi join using BETWEEN?

easy

A. SELECT * FROM A JOIN B ON A.value IN BETWEEN B.min AND B.max;

B. SELECT * FROM A JOIN B ON A.value = BETWEEN B.min AND B.max;

C. SELECT * FROM A JOIN B ON BETWEEN A.value AND B.min AND B.max;

D. SELECT * FROM A JOIN B ON A.value BETWEEN B.min AND B.max;

Solution

1. Step 1: Recall BETWEEN syntax

   BETWEEN is used as: column BETWEEN low AND high, without extra operators.

2. Step 2: Check each option

   SELECT * FROM A JOIN B ON A.value BETWEEN B.min AND B.max; uses correct syntax: A.value BETWEEN B.min AND B.max. Others misuse BETWEEN or add extra operators.

3. Final Answer:

   SELECT * FROM A JOIN B ON A.value BETWEEN B.min AND B.max; -> Option D

4. Quick Check:

   BETWEEN syntax = column BETWEEN low AND high [OK]

Hint: BETWEEN syntax: column BETWEEN low AND high, no extra operators [OK]

Common Mistakes:

• Adding = before BETWEEN
• Using IN BETWEEN instead of BETWEEN
• Placing BETWEEN incorrectly in ON clause

3. Given tables Products(product_id, price) and Discounts(min_price, max_price, discount_rate), what does this query return?

SELECT p.product_id, d.discount_rate
FROM Products p
JOIN Discounts d ON p.price >= d.min_price AND p.price < d.max_price;

medium

A. Only products with price exactly equal to min_price or max_price.

B. All products joined with all discounts regardless of price.

C. All products with their matching discount rate based on price ranges.

D. Syntax error due to invalid join condition.

Solution

1. Step 1: Analyze join condition

   The join matches products where price is between min_price (inclusive) and max_price (exclusive).

2. Step 2: Understand result

   This returns products with their discount rate if their price falls in the discount's price range.

3. Final Answer:

   All products with their matching discount rate based on price ranges. -> Option C

4. Quick Check:

   Non-equi join matches price ranges = All products with their matching discount rate based on price ranges. [OK]

Hint: Non-equi join matches ranges using >= and < [OK]

Common Mistakes:

• Thinking only exact matches are returned
• Assuming all products join with all discounts
• Believing the query has syntax errors

4. Identify the error in this non-equi join query:

SELECT e.name, s.salary_grade
FROM Employees e
JOIN SalaryGrades s ON e.salary => s.min_salary AND e.salary <= s.max_salary;

medium

A. The join condition should use OR instead of AND.

B. The operator => is invalid; it should be >=.

C. The table alias 's' is missing in the SELECT clause.

D. The query is missing a WHERE clause.

Solution

1. Step 1: Check operators in join condition

   The operator => is not valid SQL; the correct operator for 'greater than or equal' is >=.

2. Step 2: Verify other parts

   AND is correct to check salary between min and max. Aliases and WHERE clause are not errors here.

3. Final Answer:

   The operator => is invalid; it should be >=. -> Option B

4. Quick Check:

   Use >=, not => for greater or equal [OK]

Hint: Use >=, not =>, for greater or equal operator [OK]

Common Mistakes:

• Typing => instead of >=
• Replacing AND with OR incorrectly
• Confusing alias usage in SELECT

5. You have a table Scores(student_id, score) and a table Grades(grade, min_score, max_score). Write a query to assign each student their grade based on their score using a non-equi join.
Which query correctly implements this?

hard

A. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score >= g.min_score AND s.score < g.max_score;

B. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score <= g.min_score AND s.score >= g.max_score;

C. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score > g.min_score AND s.score <= g.max_score;

D. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score BETWEEN g.min_score AND g.max_score;

Solution

1. Step 1: Understand grading ranges

   Grades are assigned where score is between min_score (inclusive) and max_score (exclusive) to avoid overlap.

2. Step 2: Check each join condition

   SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score >= g.min_score AND s.score < g.max_score; uses s.score >= g.min_score AND s.score < g.max_score, correctly defining non-overlapping ranges.

3. Step 3: Verify other options

   SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score BETWEEN g.min_score AND g.max_score; includes max_score in BETWEEN (inclusive), which may cause overlap. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score > g.min_score AND s.score <= g.max_score; reverses inclusivity. SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score <= g.min_score AND s.score >= g.max_score; reverses logic incorrectly.

4. Final Answer:

   SELECT s.student_id, g.grade FROM Scores s JOIN Grades g ON s.score >= g.min_score AND s.score < g.max_score; -> Option A

5. Quick Check:

   Use >= min and < max for non-overlapping ranges [OK]

Hint: Use >= min_score and < max_score for clean grade ranges [OK]

Common Mistakes:

• Using BETWEEN which includes max_score causing overlap
• Swapping < and > operators
• Using incorrect inclusivity causing duplicate grades