SUNION, SINTER, SDIFF set operations in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command SUNION do?

It returns all the unique members from all the given sets combined, like gathering all friends from different groups without repeats.

beginner

Explain the Redis command SINTER in simple terms.

It finds the common members that exist in all the given sets, like finding friends who are in every group you belong to.

beginner

What is the purpose of the Redis command SDIFF?

It returns members from the first set that are not in the other sets, like finding friends unique to your first group and not in others.

beginner

If you run SUNION set1 set2 and set1 has {a, b} and set2 has {b, c}, what is the result?

The result is {a, b, c} because SUNION combines all unique members from both sets.

beginner

What will SINTER set1 set2 return if set1 = {x, y, z} and set2 = {y, z, w}?

It will return {y, z} because those members are common to both sets.

Which Redis command returns all unique members from multiple sets combined?

A SDIFF

B SINTER

C SUNION

D SMEMBERS

SUNION returns the union of all members from the given sets.

What does SINTER return when used on sets?

A Members common to all sets

B All members from all sets combined

C The size of the sets

D Members unique to the first set

SINTER returns members that exist in every set provided.

If set1 = {1, 2, 3} and set2 = {2, 4}, what does SDIFF set1 set2 return?

A {1, 3}

B {1, 2, 3, 4}

C {2}

D {}

SDIFF returns members in set1 not in set2, so {1, 3}.

Which command would you use to find members that are in both setA and setB?

A SUNION setA setB

B SINTER setA setB

C SDIFF setA setB

D SADD setA setB

SINTER finds the intersection (common members) of sets.

What will SUNION return if one of the sets is empty?

A Members only from the empty set

B An empty set

C Error

D Only members from the non-empty sets

SUNION returns all unique members from all sets, ignoring empty ones.

Describe in your own words what the Redis commands SUNION, SINTER, and SDIFF do with sets.

Think about combining friends from groups, common friends, and unique friends.

Give a real-life example to explain when you would use SUNION, SINTER, and SDIFF in Redis.

Imagine groups of friends or shopping lists.

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