Range queries for scoring in Redis - Step-by-Step Execution

Concept Flow - Range queries for scoring

Start with Sorted Set

↓

Specify Score Range

↓

Execute ZRANGEBYSCORE

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Redis Filters Members by Score

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Return Members in Score Range

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End

This flow shows how Redis uses ZRANGEBYSCORE to get members from a sorted set within a score range.

Execution Sample

Redis

ZADD players 10 "Alice" 20 "Bob" 30 "Charlie"
ZRANGEBYSCORE players 15 30

Add players with scores, then get players with scores between 15 and 30.

Execution Table

Step	Command	Action	Score Range	Result
1	ZADD players 10 "Alice" 20 "Bob" 30 "Charlie"	Add members with scores	-	Added 3 members
2	ZRANGEBYSCORE players 15 30	Query members with scores >=15 and <=30	15 to 30	["Bob", "Charlie"]
3	ZRANGEBYSCORE players (10 20	Query members with scores >10 and <=20	>10 to 20	["Bob"]
4	ZRANGEBYSCORE players -inf 25	Query members with scores <=25	-inf to 25	["Alice", "Bob"]
5	ZRANGEBYSCORE players 31 +inf	Query members with scores >=31	31 to +inf	[]
6	Exit	No more queries	-	End of range queries

💡 All range queries executed, no more matching members or queries.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5	Final
players	empty	{"Alice":10, "Bob":20, "Charlie":30}	{"Alice":10, "Bob":20, "Charlie":30}	{"Alice":10, "Bob":20, "Charlie":30}	{"Alice":10, "Bob":20, "Charlie":30}	{"Alice":10, "Bob":20, "Charlie":30}	{"Alice":10, "Bob":20, "Charlie":30}
query_result	none	none	["Bob", "Charlie"]	["Bob"]	["Alice", "Bob"]	[]	none

Key Moments - 2 Insights

Why does the query ZRANGEBYSCORE players (10 20 exclude Alice but include Bob?

Because (10 means scores strictly greater than 10, so Alice with score 10 is excluded, but Bob with 20 is included as 20 <= 20.

What happens if the score range has -inf or +inf?

Redis treats -inf as the lowest possible score and +inf as the highest, so it includes all members below or above those bounds respectively, as shown in steps 4 and 5.

Visual Quiz - 3 Questions

Look at the execution table, what is the result of ZRANGEBYSCORE players 15 30 at step 2?

A ["Bob", "Charlie"]

B ["Alice", "Bob"]

C ["Alice", "Charlie"]

D []

💡 Hint

Check the 'Result' column in row for step 2 in execution_table.

At which step does the query return an empty list?

A Step 4

B Step 3

C Step 5

D Step 2

💡 Hint

Look for [] in the 'Result' column in execution_table.

If we change the query in step 3 to ZRANGEBYSCORE players 10 20 (without parentheses), what will be included?

A Only Bob

B Alice and Bob

C Only Alice

D Alice, Bob, and Charlie

💡 Hint

Parentheses mean exclusive, no parentheses mean inclusive; check step 3 query and results.

Concept Snapshot

Redis ZRANGEBYSCORE command:
Syntax: ZRANGEBYSCORE key min max
Returns members with scores between min and max.
Use ( before number for exclusive range.
-min and +max mean unbounded range.
Useful for filtering sorted sets by score.

Full Transcript

This visual execution trace shows how Redis handles range queries for scoring using the ZRANGEBYSCORE command. First, members with scores are added to a sorted set. Then queries specify score ranges to retrieve members within those scores. The trace shows inclusive and exclusive ranges, unbounded ranges using -inf and +inf, and the results returned. Key moments clarify how exclusive ranges exclude boundary scores and how infinite bounds work. The quiz tests understanding of results at different steps and the effect of parentheses on score ranges.

Practice

1. What does the Redis command ZRANGEBYSCORE do?

easy

A. It returns members in a sorted set within a specified score range.

B. It deletes members from a sorted set based on score.

C. It adds new members to a sorted set with scores.

D. It returns the total number of members in a sorted set.

Solution

1. Step 1: Understand the command purpose

   ZRANGEBYSCORE is used to get members from a sorted set filtered by score range.

2. Step 2: Compare options with command behavior

   Only "It returns members in a sorted set within a specified score range." correctly describes returning members within a score range.

3. Final Answer:

   It returns members in a sorted set within a specified score range. -> Option A

4. Quick Check:

   ZRANGEBYSCORE = returns members by score range [OK]

Hint: ZRANGEBYSCORE fetches members filtered by score range [OK]

Common Mistakes:

• Confusing ZRANGEBYSCORE with commands that add or delete members
• Thinking it returns count instead of members
• Assuming it sorts members by name instead of score

2. Which of the following is the correct syntax to get members with scores between 10 and 20 from a sorted set named myzset?

easy

A. ZRANGEBYSCORE myzset [10 [20

B. ZRANGEBYSCORE myzset (10 (20

C. ZRANGEBYSCORE myzset 10 20

D. ZRANGEBYSCORE myzset "10" "20"

Solution

1. Step 1: Recall basic syntax of ZRANGEBYSCORE

   The command format is ZRANGEBYSCORE key min max where min and max are numbers or special strings.

2. Step 2: Analyze options for correct syntax

   ZRANGEBYSCORE myzset 10 20 uses plain numbers 10 and 20 correctly. Options A and B use parentheses or brackets which mean exclusive or inclusive but are not needed here. ZRANGEBYSCORE myzset "10" "20" uses quotes which are unnecessary.

3. Final Answer:

   ZRANGEBYSCORE myzset 10 20 -> Option C

4. Quick Check:

   Syntax = ZRANGEBYSCORE key min max [OK]

Hint: Use plain numbers for inclusive score range in ZRANGEBYSCORE [OK]

Common Mistakes:

• Using parentheses or brackets incorrectly for inclusive ranges
• Adding quotes around numeric scores
• Mixing up min and max order

3. Given the sorted set myzset with members and scores: {"a":5, "b":10, "c":15, "d":20}, what is the result of ZRANGEBYSCORE myzset 10 20 WITHSCORES?

medium

A. ["b", "10", "c", "15", "d", "20"]

B. ["a", "5", "b", "10", "c", "15"]

C. ["c", "15", "d", "20"]

D. ["a", "5", "d", "20"]

Solution

1. Step 1: Identify members with scores between 10 and 20 inclusive

   Members with scores 10, 15, and 20 are "b", "c", and "d" respectively.

2. Step 2: Understand WITHSCORES option output

   WITHSCORES returns members and their scores as alternating elements in the list.

3. Final Answer:

   ["b", "10", "c", "15", "d", "20"] -> Option A

4. Quick Check:

   Members with scores 10-20 + WITHSCORES = ["b", "10", "c", "15", "d", "20"] [OK]

Hint: WITHSCORES returns member-score pairs in order [OK]

Common Mistakes:

• Including members outside the score range
• Returning only members without scores
• Mixing order of members and scores

4. What is wrong with this command to get members with scores between 5 and 15 from myzset?

ZRANGEBYSCORE myzset 5 15 WITHSCORE

medium

A. The score range should be reversed as 15 5.

B. The option should be WITHSCORES, not WITHSCORE.

C. The command needs a LIMIT clause to work.

D. The key name must be quoted.

Solution

1. Step 1: Check the option spelling

   The correct option to include scores is WITHSCORES (plural), not WITHSCORE.

2. Step 2: Verify other parts of the command

   The score range 5 to 15 is correct, LIMIT is optional, and key names do not require quotes.

3. Final Answer:

   The option should be WITHSCORES, not WITHSCORE. -> Option B

4. Quick Check:

   Correct option spelling = WITHSCORES [OK]

Hint: Use WITHSCORES (plural) to get scores with members [OK]

Common Mistakes:

• Misspelling WITHSCORES option
• Reversing min and max scores
• Adding unnecessary quotes around key

5. You have a sorted set players with player names and their scores. You want to find all players with scores greater than 50 but less than or equal to 100, including their scores. Which command correctly achieves this?

hard

A. ZRANGEBYSCORE players [50 100 WITHSCORES

B. ZRANGEBYSCORE players 50 100 WITHSCORES

C. ZRANGEBYSCORE players (50 (100 WITHSCORES

D. ZRANGEBYSCORE players (50 100 WITHSCORES

Solution

1. Step 1: Understand score range requirements

   Scores must be greater than 50 (exclusive) and less than or equal to 100 (inclusive).

2. Step 2: Use parentheses for exclusive and plain number for inclusive

   In Redis, (50 means greater than 50 (exclusive), and 100 means less than or equal to 100 (inclusive).

3. Step 3: Check command syntax

   ZRANGEBYSCORE players (50 100 WITHSCORES correctly uses (50 and 100 with WITHSCORES option.

4. Final Answer:

   ZRANGEBYSCORE players (50 100 WITHSCORES -> Option D

5. Quick Check:

   Exclusive lower bound uses (number) syntax [OK]

Hint: Use (number for exclusive, number for inclusive in range [OK]

Common Mistakes:

• Using brackets [] which Redis does not support for range
• Not using parentheses for exclusive bounds
• Confusing inclusive and exclusive range syntax