SUNION, SINTER, SDIFF set operations in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of SUNION on two sets?

Given two Redis sets:

Set A contains: {"apple", "banana", "cherry"}
Set B contains: {"banana", "date", "fig"}

What is the result of SUNION A B?

Redis

SADD A apple banana cherry
SADD B banana date fig
SUNION A B

A ["banana"]

B ["apple", "banana", "cherry"]

C ["apple", "banana", "cherry", "date", "fig"]

D ["date", "fig"]

💡 Hint

SUNION returns all unique members from both sets combined.

SUNION combines all unique elements from both sets. Since 'banana' is in both, it appears once. The result includes all unique fruits from both sets.

❓ query_result

intermediate

What does SINTER return for overlapping sets?

Given two Redis sets:

Set X contains: {"red", "blue", "green"}
Set Y contains: {"blue", "yellow", "green"}

What is the output of SINTER X Y?

Redis

SADD X red blue green
SADD Y blue yellow green
SINTER X Y

A ["blue", "green"]

B ["red", "yellow"]

C ["red", "blue", "green", "yellow"]

D []

💡 Hint

SINTER returns only members present in both sets.

SINTER returns the intersection of the sets, which are the elements present in both X and Y: blue and green.

❓ query_result

advanced

What is the output of SDIFF with three sets?

Given three Redis sets:

Set M contains: {"cat", "dog", "rabbit"}
Set N contains: {"dog", "hamster"}
Set O contains: {"rabbit", "parrot"}

What is the result of SDIFF M N O?

Redis

SADD M cat dog rabbit
SADD N dog hamster
SADD O rabbit parrot
SDIFF M N O

A ["rabbit"]

B ["dog", "cat"]

C ["hamster", "parrot"]

D ["cat"]

💡 Hint

SDIFF returns members in the first set that are not in any of the other sets.

SDIFF returns elements in M that are not in N or O. 'cat' is only in M, so it is returned.

🧠 Conceptual

advanced

Which Redis command would you use to find common elements between sets?

You want to find elements that exist in all given Redis sets. Which command should you use?

A SINTER

B SDIFF

C SUNION

D SMEMBERS

💡 Hint

Think about which command returns only shared members.

SINTER returns the intersection of sets, i.e., elements common to all sets.

📝 Syntax

expert

Identify the syntax error in this Redis command usage

Consider the following Redis command:

SDIFFSET myset otherset

What is wrong with this command?

A The command requires only one key, but two are given.

B The command name is incorrect; it should be SDIFFSTORE.

C The command should be SUNIONSET instead of SDIFFSET.

D The command is correct and will run without errors.

💡 Hint

Check the exact spelling of Redis commands for set operations.

The correct command to store the difference of sets is SDIFFSTORE, not SDIFFSET.

Practice

1. What does the Redis command SUNION do when applied to multiple sets?

easy

A. It returns all unique elements from all given sets combined.

B. It returns only the elements common to all given sets.

C. It returns elements unique to the first set only.

D. It deletes all the given sets from the database.

Solution

1. Step 1: Understand SUNION operation

   The SUNION command merges all elements from the given sets and removes duplicates.

2. Step 2: Compare with other set operations

   SINTER returns only common elements, SDIFF returns unique elements from the first set, so SUNION is the only one that merges all uniquely.

3. Final Answer:

   It returns all unique elements from all given sets combined. -> Option A

4. Quick Check:

   SUNION = all unique elements combined [OK]

Hint: SUNION combines all sets without duplicates [OK]

Common Mistakes:

• Confusing SUNION with SINTER (common elements)
• Thinking SUNION returns only first set elements
• Assuming SUNION deletes sets

2. Which of the following is the correct syntax to find the intersection of two sets set1 and set2 in Redis?

easy

A. SINTER set1 set2

B. SUNION set1 set2

C. SDIFF set1 set2

D. SINTERSECTION set1 set2

Solution

1. Step 1: Recall Redis command for intersection

   The correct Redis command to find common elements is SINTER.

2. Step 2: Check syntax correctness

   The syntax is SINTER key1 key2 .... SINTER set1 set2 matches this exactly.

3. Final Answer:

   SINTER set1 set2 -> Option A

4. Quick Check:

   SINTER syntax = SINTER keys [OK]

Hint: Use SINTER for intersection syntax [OK]

Common Mistakes:

• Using SUNION instead of SINTER
• Using non-existent command SINTERSECTION
• Confusing SDIFF with intersection

3. Given the following Redis sets:
set1 = {"apple", "banana", "cherry"}
set2 = {"banana", "date", "fig"}
What is the result of SINTER set1 set2?

medium

A. ["apple", "banana", "cherry", "date", "fig"]

B. ["banana"]

C. ["apple", "cherry"]

D. ["date", "fig"]

Solution

1. Step 1: Identify common elements between set1 and set2

   Elements in set1: apple, banana, cherry; set2: banana, date, fig. The only common element is banana.

2. Step 2: Understand SINTER output

   SINTER returns only elements present in all sets, so the result is ["banana"].

3. Final Answer:

   ["banana"] -> Option B

4. Quick Check:

   SINTER common elements = ["banana"] [OK]

Hint: SINTER returns only common elements [OK]

Common Mistakes:

• Listing all elements instead of common ones
• Confusing SINTER with SUNION or SDIFF
• Including elements unique to one set

4. You run the command SDIFF set1 set2 but get an unexpected empty result. Given:
set1 = {"cat", "dog"}
set2 = {"cat", "dog", "mouse"}
What is the likely reason?

medium

A. set1 is empty, so SDIFF returns empty.

B. SDIFF syntax requires only one set argument.

C. Redis does not support SDIFF with these sets.

D. All elements of set1 are also in set2, so no unique elements remain.

Solution

1. Step 1: Understand SDIFF behavior

   SDIFF returns elements in the first set that are not in the other sets.

2. Step 2: Analyze given sets

   set1 has "cat" and "dog"; set2 has "cat", "dog", and "mouse". Since all set1 elements are in set2, SDIFF returns an empty set.

3. Final Answer:

   All elements of set1 are also in set2, so no unique elements remain. -> Option D

4. Quick Check:

   SDIFF unique first set elements = empty [OK]

Hint: SDIFF returns only unique first set elements [OK]

Common Mistakes:

• Assuming SDIFF requires only one set
• Thinking SDIFF returns common elements
• Believing Redis lacks SDIFF support

5. You have three Redis sets:
setA = {"red", "blue", "green"}
setB = {"blue", "yellow"}
setC = {"green", "yellow", "black"}
Which command returns elements that are in setA but not in setB or setC?

hard

A. SUNION setA setB setC

B. SINTER setA setB setC

C. SDIFF setA setB setC

D. SDIFF setB setA setC

Solution

1. Step 1: Understand SDIFF with multiple sets

   SDIFF returns elements in the first set that are not in any of the other sets.

2. Step 2: Apply SDIFF to given sets

   Elements in setA: red, blue, green. Elements in setB and setC combined: blue, yellow, green, black. Elements unique to setA are only "red".

3. Step 3: Verify command correctness

   SDIFF setA setB setC uses SDIFF with setA first, then setB and setC, which matches the requirement.

4. Final Answer:

   SDIFF setA setB setC -> Option C

5. Quick Check:

   SDIFF first set minus others = unique elements [OK]

Hint: Use SDIFF with first set then others to find unique elements [OK]

Common Mistakes:

• Using SINTER or SUNION instead of SDIFF
• Reversing set order in SDIFF
• Expecting SDIFF to return common elements