SUNIONSTORE for storing results in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command SUNIONSTORE do?

It creates a new set by combining all unique members from given sets and stores the result in a specified destination key.

beginner

How do you use SUNIONSTORE to combine sets set1 and set2 into resultSet?

Use the command: SUNIONSTORE resultSet 2 set1 set2. This stores the union of set1 and set2 in resultSet.

intermediate

What happens if the destination key in SUNIONSTORE already exists?

The existing key is overwritten with the new union set.

beginner

Can SUNIONSTORE be used with just one set?

Yes, but it simply copies that set to the destination key.

beginner

What type of data structure does SUNIONSTORE work with in Redis?

It works only with sets, which are collections of unique strings.

What does SUNIONSTORE dest set1 set2 do?

A Stores the intersection of set1 and set2 in dest

B Stores the union of set1 and set2 in dest

C Deletes set1 and set2

D Copies set1 to set2

SUNIONSTORE combines all unique members from the given sets and stores them in the destination key.

If dest already exists, what happens when you run SUNIONSTORE dest set1 set2?

A dest is deleted

B An error occurs

C dest is overwritten with the union

D dest remains unchanged

The existing dest key is overwritten with the new union set.

Which Redis data type is required for SUNIONSTORE?

A Sets

B Hashes

C Strings

D Lists

SUNIONSTORE works only with sets.

What result does SUNIONSTORE dest set1 produce?

A Copies set1 to dest

B Deletes set1

C Creates an empty set

D Throws an error

Using one set copies it to the destination key.

Which command would you use to combine multiple sets and save the result in Redis?

A SADD

B SINTERSTORE

C SMEMBERS

D SUNIONSTORE

SUNIONSTORE combines sets and stores the union.

Explain how the Redis command SUNIONSTORE works and when you would use it.

Think about combining unique items from different groups and saving them.

Describe what happens if the destination key already exists when using SUNIONSTORE.

Consider how Redis handles keys when storing new data.

Practice

1. What does the Redis command SUNIONSTORE destination key1 key2 do?

easy

A. It merges the sets stored at key1 and key2 and stores the result in destination.

B. It deletes the sets at key1 and key2 and creates a new set at destination.

C. It returns the union of sets at key1 and key2 without storing it.

D. It copies the set at key1 to destination without merging.

Solution

1. Step 1: Understand SUNIONSTORE purpose

   The command merges multiple sets into one combined set.

2. Step 2: Identify storage behavior

   The result is stored in the specified destination key, overwriting if it exists.

3. Final Answer:

   It merges the sets stored at key1 and key2 and stores the result in destination. -> Option A

4. Quick Check:

   SUNIONSTORE merges and stores = C [OK]

Hint: SUNIONSTORE merges sets and saves result in destination [OK]

Common Mistakes:

• Confusing SUNIONSTORE with SUNION (which does not store)
• Thinking it deletes original sets
• Assuming it copies only one set

2. Which of the following is the correct syntax to store the union of sets setA and setB into resultSet using Redis?

easy

A. SUNIONSTORE setA setB resultSet

B. SUNIONSTORE resultSet setA setB

C. SUNION resultSet setA setB

D. SUNIONSTORE setA resultSet setB

Solution

1. Step 1: Recall SUNIONSTORE syntax

   The correct syntax is SUNIONSTORE destination key1 key2 ....

2. Step 2: Match keys to syntax

   Here, resultSet is destination, followed by sets setA and setB.

3. Final Answer:

   SUNIONSTORE resultSet setA setB -> Option B

4. Quick Check:

   Destination first, then sets = A [OK]

Hint: Destination key comes first in SUNIONSTORE command [OK]

Common Mistakes:

• Placing destination key last
• Using SUNION instead of SUNIONSTORE for storing
• Mixing order of keys

3. You have three sets:
setX = {1, 2, 3}
setY = {3, 4, 5}
setZ = {5, 6}
You want to create a new set combined that contains the union of all three sets. Which command correctly does this and stores the result in combined?

easy

A. SUNIONSTORE combined setX setY setZ

B. SUNIONSTORE combined setX setY

C. SUNION combined setX setY setZ

D. SUNIONSTORE setX setY setZ combined

Solution

1. Step 1: Recall SUNIONSTORE usage for multiple sets

   SUNIONSTORE can take multiple keys after the destination key.

2. Step 2: Verify correct order and keys

   Destination is combined, followed by setX, setY, and setZ.

3. Final Answer:

   SUNIONSTORE combined setX setY setZ -> Option A

4. Quick Check:

   Destination first, then all sets = B [OK]

Hint: List all sets after destination in SUNIONSTORE [OK]

Common Mistakes:

• Using SUNION instead of SUNIONSTORE to store
• Placing destination key last
• Omitting one or more sets

4. Given the following Redis sets:
SADD set1 a b c
SADD set2 b c d
What will be the members of resultSet after executing SUNIONSTORE resultSet set1 set2?

medium

A. ["a", "d"]

B. ["a", "b", "c"]

C. ["a", "b", "c", "d"]

D. ["b", "c", "d"]

Solution

1. Step 1: Identify members of each set

   set1 has {a, b, c}, set2 has {b, c, d}.

2. Step 2: Compute union of both sets

   The union is {a, b, c, d} combining all unique members.

3. Final Answer:

   ["a", "b", "c", "d"] -> Option C

4. Quick Check:

   Union of set1 and set2 = ["a", "b", "c", "d"] [OK]

Hint: Union combines all unique elements from both sets [OK]

Common Mistakes:

• Forgetting to include all unique elements
• Confusing union with intersection
• Assuming order matters in sets

5. You run the command SUNIONSTORE result set1 set2 but get an error. What is the most likely cause?

medium

A. SUNIONSTORE does not accept more than two sets.

B. You forgot to specify the destination key.

C. The sets set1 and set2 do not exist.

D. The key result already exists as a string, not a set.

Solution

1. Step 1: Understand data type requirements

   SUNIONSTORE requires the destination key to be a set or not exist.

2. Step 2: Identify error cause

   If result exists as a string or other type, Redis throws a type error.

3. Final Answer:

   The key result already exists as a string, not a set. -> Option D

4. Quick Check:

   Destination key type mismatch causes error [OK]

Hint: Destination key must be a set or not exist [OK]

Common Mistakes:

• Assuming missing keys cause errors (they don't)
• Thinking SUNIONSTORE limits number of sets
• Ignoring key data types