Range queries for scoring in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What Redis data structure is commonly used for range queries based on scores?

Redis Sorted Sets are used for range queries based on scores because they store members ordered by their score values.

beginner

Which Redis command retrieves members with scores between a minimum and maximum value?

The command ZRangeByScore retrieves members with scores within a specified range.

intermediate

How do you include the scores in the results when performing a range query in Redis?

Use the WITHSCORES option with ZRangeByScore to get both members and their scores.

intermediate

What symbol do you use in Redis range queries to represent negative or positive infinity?

Use -inf for negative infinity and +inf for positive infinity to specify open-ended ranges.

intermediate

How can you limit the number of results returned by a Redis range query?

Use the LIMIT offset count option with ZRangeByScore to restrict the number of returned members.

Which Redis command fetches members with scores between 10 and 20?

A ZSCORE key 10 20

B ZRANGE key 10 20

C ZRANGEBYSCORE key 10 20

D ZGETRANGE key 10 20

ZRANGEBYSCORE is the correct command to fetch members within a score range.

How do you get the scores along with members in a range query?

A Add WITHSCORES option

B Add GETSCORES option

C Add SHOWSCORES option

D Add SCORES option

The WITHSCORES option returns scores with members.

What does -inf mean in a Redis range query?

A Zero score

B Negative infinity, lowest possible score

C Positive infinity, highest possible score

D No score

-inf represents negative infinity, meaning no lower limit.

Which option limits the number of results in ZRangeByScore?

A LIMIT offset count

B COUNT offset limit

C MAX offset count

D OFFSET limit count

LIMIT offset count restricts the number of returned members.

If you want all members with scores greater than or equal to 50, what is the correct range?

A -inf +inf

B -inf 50

C 0 50

D 50 +inf

Using 50 +inf fetches all members with scores from 50 upwards.

Explain how to perform a range query in Redis to get members with scores between two values, including how to get their scores and limit results.

Think about the command and options you add for scores and limits.

Describe the meaning and use of -inf and +inf in Redis range queries.

They help when you want to query from or up to any score.

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