HINCRBY for numeric fields in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

What is the result of this HINCRBY command?

Given a Redis hash key user:1000 with field score set to 10, what will be the value of score after running HINCRBY user:1000 score 5?

Redis

HSET user:1000 score 10
HINCRBY user:1000 score 5
HGET user:1000 score

A 15

B 5

C 10

D Error: field is not an integer

💡 Hint

HINCRBY adds the increment to the current integer value stored in the field.

HINCRBY increments the numeric value stored in the specified field by the given amount. Starting from 10, adding 5 results in 15.

❓ query_result

intermediate

What happens if the field does not exist?

If the Redis hash user:1001 does not have the field points, what will be the result of HINCRBY user:1001 points 7?

Redis

HINCRBY user:1001 points 7
HGET user:1001 points

A 0

B 7

C Error: field does not exist

D null

💡 Hint

HINCRBY treats missing fields as zero before incrementing.

If the field does not exist, Redis treats its value as 0 and increments by the given amount, so the new value is 7.

📝 Syntax

advanced

Which HINCRBY command is syntactically correct?

Choose the correct syntax to increment the field level by 3 in the hash game:player1.

A HINCRBY level game:player1 3

B HINCRBY game:player1 level

C HINCRBY game:player1 3 level

D HINCRBY game:player1 level 3

💡 Hint

The syntax is HINCRBY key field increment.

The correct syntax is HINCRBY followed by the key, then the field, then the increment number.

❓ query_result

advanced

What error occurs if the field contains a non-integer value?

If the field score in hash user:1002 contains the string ten, what happens when running HINCRBY user:1002 score 1?

Redis

HSET user:1002 score ten
HINCRBY user:1002 score 1

A Error: hash value is not an integer

B score becomes 1

C score becomes 'ten1'

D score becomes 11

💡 Hint

HINCRBY requires the field value to be an integer string.

If the field value is not an integer string, HINCRBY returns an error.

🧠 Conceptual

expert

Why is HINCRBY preferred over GET and SET for incrementing numeric fields?

Consider incrementing a numeric field in a Redis hash. Why is using HINCRBY better than using HGET to get the value, incrementing it in the client, and then HSET to update it?

A GET and SET commands do not work on hash fields.

B HINCRBY is slower but more readable than GET and SET.

C HINCRBY is atomic, preventing race conditions in concurrent environments.

D HINCRBY automatically converts strings to integers.

💡 Hint

Think about what happens if multiple clients increment at the same time.

HINCRBY performs the increment atomically inside Redis, avoiding race conditions that can happen if you GET, increment, and SET separately.