ZADD for adding scored members in Redis - Step-by-Step Execution

Concept Flow - ZADD for adding scored members

Start ZADD command

↓

Parse key and score-member pairs

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Check if sorted set exists

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Add/update members with scores

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Return number of new elements added

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End

ZADD adds members with scores to a sorted set, creating it if missing, and returns how many new members were added.

Execution Sample

Redis

ZADD myset 10 "apple" 20 "banana" 15 "cherry"

Adds three members with scores to the sorted set 'myset'.

Execution Table

Step	Action	Key State Before	Members Added/Updated	Key State After	Return Value
1	Start ZADD command	myset does not exist	None	myset created empty	None
2	Add member 'apple' with score 10	empty	apple added	{"apple":10}	1
3	Add member 'banana' with score 20	{"apple":10}	banana added	{"apple":10, "banana":20}	2
4	Add member 'cherry' with score 15	{"apple":10, "banana":20}	cherry added	{"apple":10, "banana":20, "cherry":15}	3
5	Return total new members added	{"apple":10, "banana":20, "cherry":15}	None	{"apple":10, "banana":20, "cherry":15}	3

💡 All members processed, ZADD returns count of new members added (3).

Variable Tracker

Variable	Start	After 1	After 2	After 3	Final
myset	does not exist	{"apple":10}	{"apple":10, "banana":20}	{"apple":10, "banana":20, "cherry":15}	{"apple":10, "banana":20, "cherry":15}
new_members_count	0	1	2	3	3

Key Moments - 2 Insights

Why does ZADD create the sorted set if it does not exist?

Because the execution_table row 1 shows the key 'myset' does not exist initially, ZADD creates it to add members.

What does the return value represent in ZADD?

As seen in execution_table rows 2-5, the return value counts how many new members were added, not updated.

Visual Quiz - 3 Questions

Look at the execution_table, what is the state of 'myset' after step 2?

A {"apple":10}

B {"banana":20}

C empty

D does not exist

💡 Hint

Check the 'Key State After' column in row 2 of the execution_table.

At which step does ZADD add the member 'cherry'?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Action' column in the execution_table for when 'cherry' is added.

If 'banana' was already in 'myset' with score 20, what would the return value be after adding it again with the same score?

A 1

B 2

C 0

D 3

💡 Hint

Recall that ZADD returns the count of new members added, not updated ones, as shown in the variable_tracker.

Concept Snapshot

ZADD key score member [score member ...]
- Adds members with scores to a sorted set
- Creates the set if it doesn't exist
- Returns number of new members added
- Updates score if member exists but does not count as new
- Useful for ranking or sorted data storage

Full Transcript

ZADD is a Redis command to add members with scores to a sorted set. If the sorted set does not exist, ZADD creates it first. Each member is added with its score, and if the member already exists, its score is updated but not counted as a new addition. The command returns the number of new members added. For example, adding 'apple' with score 10, 'banana' with 20, and 'cherry' with 15 to a new sorted set 'myset' results in 'myset' containing these three members and the return value being 3. This process helps store and retrieve data sorted by scores efficiently.