ZINCRBY for score updates in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis command ZINCRBY do?

It increases the score of a member in a sorted set by a given amount. If the member does not exist, it is added with the increment as its score.

beginner

How do you increase the score of member 'player1' by 10 in a sorted set 'game_scores'?

Use the command: ZINCRBY game_scores 10 player1.

beginner

What happens if you use ZINCRBY on a member that does not exist in the sorted set?

The member is added to the sorted set with the score equal to the increment value.

intermediate

Can ZINCRBY decrease a member's score? How?

Yes, by using a negative increment value. For example, ZINCRBY game_scores -5 player1 decreases player1's score by 5.

beginner

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

It works with sorted sets, which store members ordered by their scores.

What does the Redis command ZINCRBY myset 3 member1 do?

A Removes 'member1' from 'myset'

B Adds 3 to the score of 'member1' in 'myset', or adds 'member1' with score 3 if not present

C Sets the score of 'member1' to 3 in 'myset' regardless of previous score

D Returns the current score of 'member1' in 'myset'

ZINCRBY increases the score of the member by the given increment or adds it with that score if it doesn't exist.

If you run ZINCRBY leaderboard -2 player42, what happens?

A The score of 'player42' increases by 2

B 'player42' is removed from 'leaderboard'

C An error occurs because increment cannot be negative

D The score of 'player42' decreases by 2

ZINCRBY accepts negative increments to decrease a member's score.

Which Redis data type is required to use ZINCRBY?

A List

B Hash

C Sorted Set

D String

ZINCRBY works only with sorted sets.

What will ZINCRBY scores 5 newplayer do if 'newplayer' is not in 'scores'?

A Add 'newplayer' with score 5

B Add 'newplayer' with score 0

C Do nothing

D Return an error

If the member does not exist, ZINCRBY adds it with the increment as its score.

What does the return value of ZINCRBY represent?

A The new score of the member after increment

B The old score before increment

C The total number of members in the sorted set

D The rank of the member in the sorted set

ZINCRBY returns the updated score of the member.

Explain how the Redis command ZINCRBY updates scores in a sorted set.

Think about how scores change and what happens if the member is new.

Describe a real-life example where you might use ZINCRBY in a Redis sorted set.

Imagine a game where players earn points over time.

Practice

1.

What does the Redis command ZINCRBY do?

easy

A. It creates a new sorted set without any members.

B. It increases the score of a member in a sorted set by a given amount.

C. It returns the rank of a member in a sorted set.

D. It deletes a member from a sorted set.

Solution

1. Step 1: Understand the purpose of ZINCRBY

   ZINCRBY is used to increase the score of a member in a sorted set by a specified increment.

2. Step 2: Compare with other options

   Other options describe different commands: deletion, rank retrieval, or creation, which are not what ZINCRBY does.

3. Final Answer:

   It increases the score of a member in a sorted set by a given amount. -> Option B

4. Quick Check:

   ZINCRBY increments score of member [OK]

Hint: ZINCRBY always adds to a member's score in sorted sets [OK]

Common Mistakes:

• Confusing ZINCRBY with ZREM (removal)
• Thinking it returns rank instead of updating score
• Assuming it creates a new sorted set without members

2.

Which of the following is the correct syntax to increase the score of member user1 by 5 in sorted set leaderboard?

?

easy

A. ZINCRBY leaderboard 5 user1

B. ZINCRBY leaderboard user1 5

C. ZINCRBY 5 leaderboard user1

D. ZINCRBY user1 leaderboard 5

Solution

1. Step 1: Recall ZINCRBY syntax

   The correct syntax is: ZINCRBY key increment member.

2. Step 2: Match syntax with options

   ZINCRBY leaderboard 5 user1 matches the correct order: ZINCRBY leaderboard 5 user1.

3. Final Answer:

   ZINCRBY leaderboard 5 user1 -> Option A

4. Quick Check:

   Command order = ZINCRBY key increment member [OK]

Hint: Remember: ZINCRBY key increment member [OK]

Common Mistakes:

• Swapping member and increment positions
• Putting member before key
• Using increment before key

3.

Given the following Redis commands executed in order:

ZINCRBY scores 10 alice
ZINCRBY scores 5 bob
ZINCRBY scores -3 alice
ZINCRBY scores 2 charlie

What is the score of alice after these commands?

medium

A. 7

B. 10

C. 12

D. -3

Solution

1. Step 1: Calculate alice's score changes

   First increment: +10, then decrement: -3, total = 10 - 3 = 7.

2. Step 2: Confirm final score

   Other members' scores do not affect alice's score.

3. Final Answer:

   7 -> Option A

4. Quick Check:

   10 - 3 = 7 [OK]

Hint: Add increments for the same member to get final score [OK]

Common Mistakes:

• Ignoring negative increments
• Adding scores of other members
• Using only the first increment

4.

What is wrong with this Redis command to increase user2's score by 4 in sorted set game_scores?

ZINCRBY game_scores user2 4

medium

A. The increment value must be negative.

B. The key name is missing.

C. The command should be ZADD instead of ZINCRBY.

D. The increment and member arguments are swapped.

Solution

1. Step 1: Check argument order for ZINCRBY

   ZINCRBY syntax is: ZINCRBY key increment member. Here, 'user2' and '4' are swapped.

2. Step 2: Identify the error

   The command should be: ZINCRBY game_scores 4 user2.

3. Final Answer:

   The increment and member arguments are swapped. -> Option D

4. Quick Check:

   Order must be key, increment, member [OK]

Hint: Increment always comes before member in ZINCRBY [OK]

Common Mistakes:

• Swapping increment and member
• Using ZADD instead of ZINCRBY for increment
• Thinking increment must be negative

5.

You have a sorted set ranking with members and scores:

"alice" 15
"bob" 20
"carol" 10

You want to increase carol's score by 12 and decrease bob's score by 5 using Redis commands. Which sequence of commands correctly updates the scores?

hard

A. ZADD ranking 22 carol
ZADD ranking 15 bob

B. ZINCRBY ranking carol 12
ZINCRBY ranking bob -5

C. ZINCRBY ranking 12 carol
ZINCRBY ranking -5 bob

D. ZINCRBY ranking 5 carol
ZINCRBY ranking -12 bob

Solution

1. Step 1: Apply correct ZINCRBY syntax for increments

   To increase carol's score by 12: ZINCRBY ranking 12 carol.

2. Step 2: Apply correct ZINCRBY syntax for decrement

   To decrease bob's score by 5: ZINCRBY ranking -5 bob.

3. Step 3: Verify other options

   ZINCRBY ranking carol 12 ZINCRBY ranking bob -5 swaps increment and member, ZADD ranking 22 carol ZADD ranking 15 bob uses ZADD which replaces scores, ZINCRBY ranking 5 carol ZINCRBY ranking -12 bob uses wrong increments.

4. Final Answer:

   ZINCRBY ranking 12 carol ZINCRBY ranking -5 bob -> Option C

5. Quick Check:

   Use ZINCRBY with positive and negative increments [OK]

Hint: Use positive or negative increments with ZINCRBY to adjust scores [OK]

Common Mistakes:

• Swapping member and increment arguments
• Using ZADD which overwrites scores instead of incrementing
• Using wrong increment values