ZINCRBY for score updates in Redis - Step-by-Step Execution

Concept Flow - ZINCRBY for score updates

Start with Sorted Set

↓

Call ZINCRBY with key, increment, member

↓

Check if member exists in Sorted Set

Yes No↓

Increase score

↓

Update Sorted Set with new score

↓

Return new score of member

↓

End

ZINCRBY updates the score of a member in a sorted set by adding the increment. If the member does not exist, it is added with the increment as its score.

Execution Sample

Redis

ZINCRBY leaderboard 10 "player1"
ZINCRBY leaderboard 5 "player2"
ZINCRBY leaderboard -3 "player1"

This code increases player1's score by 10, adds player2 with score 5, then decreases player1's score by 3.

Execution Table

Step	Command	Member Exists?	Action	New Score	Result Returned
1	ZINCRBY leaderboard 10 "player1"	No	Add member 'player1' with score 10	10	10
2	ZINCRBY leaderboard 5 "player2"	No	Add member 'player2' with score 5	5	5
3	ZINCRBY leaderboard -3 "player1"	Yes	Decrease 'player1' score by 3	7	7
4	End	-	-	-	-

💡 All commands executed; final scores updated accordingly.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
leaderboard	{}	{"player1":10}	{"player1":10, "player2":5}	{"player1":7, "player2":5}	{"player1":7, "player2":5}

Key Moments - 2 Insights

What happens if the member does not exist in the sorted set when ZINCRBY is called?

If the member does not exist, ZINCRBY adds it to the sorted set with the increment as its initial score, as shown in steps 1 and 2 of the execution_table.

Can ZINCRBY decrease a member's score?

Yes, ZINCRBY can decrease a score by using a negative increment, as shown in step 3 where 'player1' score decreases from 10 to 7.

Visual Quiz - 3 Questions

Look at the execution_table, what is the score of 'player1' after step 3?

A 7

B 10

C 5

D 3

💡 Hint

Check the 'New Score' column for step 3 in the execution_table.

At which step is 'player2' added to the leaderboard?

A Step 1

B Step 2

C Step 3

D Step 4

💡 Hint

Look at the 'Member Exists?' and 'Action' columns in the execution_table.

If we call ZINCRBY leaderboard 4 "player3" after step 3, what will happen?

A Decrease 'player2' score by 4

B Increase 'player1' score by 4

C Add 'player3' with score 4

D No change because 'player3' does not exist

💡 Hint

Refer to the concept_flow and how new members are handled when they don't exist.

Concept Snapshot

ZINCRBY key increment member
- Adds increment to member's score in sorted set
- If member missing, adds with increment as score
- Supports positive and negative increments
- Returns updated score after operation

Full Transcript

ZINCRBY is a Redis command used to update scores in a sorted set. When you call ZINCRBY with a key, an increment, and a member, it checks if the member exists. If it does, it adds the increment to the current score. If not, it adds the member with the increment as its initial score. This works for both increasing and decreasing scores. The command returns the new score after updating. For example, adding 10 to player1 when they don't exist sets their score to 10. Adding 5 to player2 adds them with score 5. Decreasing player1 by 3 changes their score from 10 to 7.