EXCEPT (MINUS) for differences in SQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to select all rows from table1 that are not in table2.

SQL

SELECT * FROM table1 [1] SELECT * FROM table2;

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

AEXCEPT

BUNION

CINTERSECT

DJOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION instead of EXCEPT returns all rows combined.

Using INTERSECT returns only common rows, not differences.

The EXCEPT keyword returns rows from the first query that are not present in the second query.

2fill in blank

medium

Complete the code to find customers in orders2023 but not in orders2022.

SQL

SELECT customer_id FROM orders2023 [1] SELECT customer_id FROM orders2022;

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

AUNION

BEXCEPT

CJOIN

DWHERE

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN will combine rows but not filter differences.

Using UNION will merge all customers, not exclude.

EXCEPT returns customers present in 2023 orders but missing in 2022 orders.

3fill in blank

hard

Fix the error in the code to get products in inventory2024 but not in inventory2023.

SQL

SELECT product_id FROM inventory2024 [1] SELECT product_id FROM inventory2023;

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

AUNION ALL

BINTERSECT

CEXCEPT

DGROUP BY

Attempts:

3 left

💡 Hint

Common Mistakes

Using UNION ALL returns all rows including duplicates.

Using INTERSECT returns only common rows, not differences.

The correct keyword to find differences is EXCEPT. UNION ALL or INTERSECT do not return differences.

4fill in blank

hard

Fill both blanks to find employees in deptA but not in deptB, selecting only their IDs and names.

SQL

SELECT [1] FROM deptA [2] SELECT employee_id, name FROM deptB;

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

Aemployee_id, name

BJOIN

CEXCEPT

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Selecting * returns all columns, which may not match second query columns.

Using JOIN does not find differences.

Select specific columns employee_id, name and use EXCEPT to find employees only in deptA.

5fill in blank

hard

Fill all three blanks to find unique product codes in warehouse1 but not in warehouse2, selecting code, name, and quantity.

SQL

SELECT [1] FROM warehouse1 [2] SELECT [3] FROM warehouse2;

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

Aproduct_code, name, quantity

BEXCEPT

DJOIN

Attempts:

3 left

💡 Hint

Common Mistakes

Using JOIN instead of EXCEPT returns combined rows, not differences.

Selecting different columns in each query causes errors.

Select matching columns product_code, name, quantity and use EXCEPT to find products only in warehouse1.

Practice

1. What does the SQL EXCEPT operator do?

easy

A. Returns rows from the first query that are not in the second query

B. Returns rows common to both queries

C. Combines all rows from both queries including duplicates

D. Deletes rows from the first table that exist in the second

Solution

1. Step 1: Understand the purpose of EXCEPT

   The EXCEPT operator compares two query results and returns only those rows that appear in the first query but not in the second.

2. Step 2: Differentiate from other set operations

   Unlike INTERSECT which returns common rows, EXCEPT returns unique rows from the first set only.

3. Final Answer:

   Returns rows from the first query that are not in the second query -> Option A

4. Quick Check:

   EXCEPT = difference = unique first query rows [OK]

Hint: EXCEPT returns what first query has but second does not [OK]

Common Mistakes:

• Confusing EXCEPT with INTERSECT
• Thinking EXCEPT deletes rows
• Assuming EXCEPT returns all combined rows

2. Which of the following is the correct syntax to find rows in table1 not in table2 using EXCEPT?

easy

A. SELECT * FROM table1 WHERE NOT IN table2;

B. SELECT * FROM table1 MINUS table2;

C. SELECT * FROM table1 EXCEPT SELECT * FROM table2;

D. SELECT * FROM table1 JOIN table2 EXCEPT;

Solution

1. Step 1: Recall correct EXCEPT syntax

   The EXCEPT operator is used between two SELECT statements: SELECT ... FROM ... EXCEPT SELECT ... FROM ....

2. Step 2: Check each option

   SELECT * FROM table1 EXCEPT SELECT * FROM table2; uses correct syntax with two SELECT statements separated by EXCEPT. SELECT * FROM table1 MINUS table2; is incorrect because MINUS requires SELECT before both tables. SELECT * FROM table1 WHERE NOT IN table2; is invalid syntax. SELECT * FROM table1 JOIN table2 EXCEPT; misuses JOIN and EXCEPT.

3. Final Answer:

   SELECT * FROM table1 EXCEPT SELECT * FROM table2; -> Option C

4. Quick Check:

   Correct EXCEPT syntax = SELECT ... EXCEPT SELECT ... [OK]

Hint: EXCEPT goes between two SELECT queries, no JOIN needed [OK]

Common Mistakes:

• Using EXCEPT without two SELECT statements
• Confusing MINUS syntax with EXCEPT
• Trying to use EXCEPT with JOIN

3. Given these tables:
table1:
id
1
2
3

table2:
id
2
4
5

What is the result of:
SELECT id FROM table1 EXCEPT SELECT id FROM table2;

medium

A. [1, 3]

B. [2]

C. [4, 5]

D. [1, 2, 3, 4, 5]

Solution

1. Step 1: Identify rows in table1

   table1 has ids 1, 2, 3.

2. Step 2: Identify rows in table2

   table2 has ids 2, 4, 5.

3. Step 3: Apply EXCEPT logic

   EXCEPT returns rows in table1 not in table2, so ids 1 and 3 remain.

4. Final Answer:

   [1, 3] -> Option A

5. Quick Check:

   table1 - table2 = [1, 3] [OK]

Hint: Subtract table2 rows from table1 rows [OK]

Common Mistakes:

• Including ids from table2
• Returning common ids instead
• Confusing EXCEPT with UNION

4. What is wrong with this query?
SELECT name FROM employees EXCEPT name FROM managers;

medium

A. EXCEPT cannot be used with column names

B. Missing SELECT keyword before second query

C. Syntax requires JOIN instead of EXCEPT

D. No error, query is correct

Solution

1. Step 1: Check syntax of EXCEPT usage

   EXCEPT requires two full SELECT statements. The second query must start with SELECT.

2. Step 2: Identify error in given query

   The second part is missing SELECT before name FROM managers, causing syntax error.

3. Final Answer:

   Missing SELECT keyword before second query -> Option B

4. Quick Check:

   EXCEPT needs two SELECTs [OK]

Hint: Always write SELECT before both queries with EXCEPT [OK]

Common Mistakes:

• Omitting SELECT in second query
• Using EXCEPT with columns only
• Confusing EXCEPT with JOIN syntax

5. You have two tables:
orders_2023 and orders_2024, both with columns order_id and customer_id.

You want to find all orders from 2023 that were NOT repeated in 2024.

Which query correctly finds these unique 2023 orders?

hard

A. SELECT order_id, customer_id FROM orders_2023 INTERSECT SELECT order_id, customer_id FROM orders_2024;

B. SELECT order_id, customer_id FROM orders_2024 EXCEPT SELECT order_id, customer_id FROM orders_2023;

C. SELECT order_id, customer_id FROM orders_2023 UNION SELECT order_id, customer_id FROM orders_2024;

D. SELECT order_id, customer_id FROM orders_2023 EXCEPT SELECT order_id, customer_id FROM orders_2024;

Solution

1. Step 1: Understand the requirement

   We want orders in 2023 that do NOT appear in 2024.

2. Step 2: Choose correct set operation

   EXCEPT returns rows in first query not in second, so orders_2023 EXCEPT orders_2024 fits.

3. Step 3: Check other options

   SELECT order_id, customer_id FROM orders_2024 EXCEPT SELECT order_id, customer_id FROM orders_2023; reverses order, giving 2024 unique orders. SELECT order_id, customer_id FROM orders_2023 INTERSECT SELECT order_id, customer_id FROM orders_2024; returns common orders. SELECT order_id, customer_id FROM orders_2023 UNION SELECT order_id, customer_id FROM orders_2024; combines all orders.

4. Final Answer:

   SELECT order_id, customer_id FROM orders_2023 EXCEPT SELECT order_id, customer_id FROM orders_2024; -> Option D

5. Quick Check:

   2023 orders minus 2024 orders = unique 2023 orders [OK]

Hint: Use EXCEPT with 2023 first, 2024 second to find unique 2023 orders [OK]

Common Mistakes:

• Swapping table order in EXCEPT
• Using INTERSECT instead of EXCEPT
• Using UNION which combines all rows