HINCRBY for numeric fields in Redis - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to increment the field 'score' by 1 in the hash 'player1'.

Redis

HINCRBY player1 score [1]

Drag options to blanks, or click blank then click option'

A-1

B1

CINCR

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using a string like 'INCR' instead of a number.

Using 0 which does not change the value.

Using a negative number when you want to increase.

The HINCRBY command increments the numeric value of a field in a hash by the given integer. Here, we want to increase 'score' by 1.

2fill in blank

medium

Complete the code to decrease the field 'lives' by 2 in the hash 'game_stats'.

Redis

HINCRBY game_stats lives [1]

Drag options to blanks, or click blank then click option'

A-2

B2

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using positive 2 which increases the value.

Using 0 which does not change the value.

To decrease a numeric field, use a negative number with HINCRBY. Here, we subtract 2 from 'lives'.

3fill in blank

hard

Fix the error in the command to increment 'points' by 5 in the hash 'user1'.

Redis

HINCRBY user1 points [1]

Drag options to blanks, or click blank then click option'

A'5'

Bfive

C5

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Putting quotes around the number.

Using words instead of numbers.

The increment value must be an integer without quotes. Using '5' or 'five' causes errors. Use 5 as a number.

4fill in blank

hard

Fill both blanks to increment 'score' by 10 and decrement 'lives' by 1 in the hash 'player2'.

Redis

HINCRBY player2 score [1]
HINCRBY player2 lives [2]

Drag options to blanks, or click blank then click option'

A10

B-1

C1

D0

Attempts:

3 left

💡 Hint

Common Mistakes

Using positive 1 instead of -1 for decrement.

Using 0 which does not change values.

Use 10 to increase 'score' and -1 to decrease 'lives'. Both are valid increments for HINCRBY.

5fill in blank

hard

Fill all three blanks to increment 'coins' by 15, decrement 'health' by 5, and increment 'level' by 2 in the hash 'game_data'.

Redis

HINCRBY game_data coins [1]
HINCRBY game_data health [2]
HINCRBY game_data level [3]

Drag options to blanks, or click blank then click option'

A5

B-5

C2

D15

Attempts:

3 left

💡 Hint

Common Mistakes

Using positive 5 instead of -5 for health decrement.

Mixing up the numbers for each field.

Increment 'coins' by 15, decrement 'health' by 5 (negative number), and increment 'level' by 2 using HINCRBY.

Practice

1. What does the Redis command HINCRBY do when used on a hash field?

easy

A. It increments or decrements the numeric value stored in the field by a given amount.

B. It deletes the field from the hash.

C. It sets the field to a new string value.

D. It returns the current value of the field without changing it.

Solution

1. Step 1: Understand the purpose of HINCRBY

   HINCRBY is designed to change numeric values inside a hash by adding or subtracting a specified number.

2. Step 2: Identify the effect on the hash field

   It modifies the existing numeric value by the given increment or decrement amount.

3. Final Answer:

   It increments or decrements the numeric value stored in the field by a given amount. -> Option A

4. Quick Check:

   HINCRBY changes numbers inside a hash = B [OK]

Hint: HINCRBY always changes numbers by adding or subtracting [OK]

Common Mistakes:

• Thinking HINCRBY deletes or resets fields
• Using HINCRBY on non-numeric fields without error
• Confusing HINCRBY with commands that just read values

2. Which of the following is the correct syntax to increment the field score by 5 in a Redis hash named player1?

easy

A. HINCRBY 5 player1 score

B. HINCRBY score player1 5

C. HINCRBY player1 5 score

D. HINCRBY player1 score 5

Solution

1. Step 1: Recall the correct order of HINCRBY arguments

   The syntax is: HINCRBY key field increment.

2. Step 2: Match the syntax to the given options

   HINCRBY player1 score 5 follows the correct order: key = player1, field = score, increment = 5.

3. Final Answer:

   HINCRBY player1 score 5 -> Option D

4. Quick Check:

   HINCRBY key field increment = A [OK]

Hint: Remember: HINCRBY key field increment [OK]

Common Mistakes:

• Swapping field and key positions
• Placing increment before field or key
• Using wrong argument order causing errors

3. Given the following Redis commands executed in order:
HSET player1 score 10
HINCRBY player1 score 7
HINCRBY player1 score -3
What is the final value of score in player1?

medium

A. 10

B. 17

C. 14

D. 7

Solution

1. Step 1: Set initial value of score

   HSET sets score to 10.

2. Step 2: Apply first increment

   HINCRBY adds 7, so score becomes 10 + 7 = 17.

3. Step 3: Apply second increment (decrement)

   HINCRBY subtracts 3, so score becomes 17 - 3 = 14.

4. Final Answer:

   14 -> Option C

5. Quick Check:

   10 + 7 - 3 = 14 [OK]

Hint: Add increments step-by-step to find final value [OK]

Common Mistakes:

• Ignoring negative increments
• Adding increments incorrectly
• Assuming initial value is zero

4. You run the command HINCRBY player1 level 1 but get an error. The field level currently holds the string value beginner. What is the cause of the error?

medium

A. The increment value must be a string, not a number.

B. HINCRBY cannot increment a field with a non-numeric value.

C. The key player1 does not exist.

D. HINCRBY requires the field to be empty before incrementing.

Solution

1. Step 1: Check the field value type

   The field level contains a non-numeric string "beginner".

2. Step 2: Understand HINCRBY requirements

   HINCRBY only works on fields with numeric values; it cannot increment strings.

3. Final Answer:

   HINCRBY cannot increment a field with a non-numeric value. -> Option B

4. Quick Check:

   Non-numeric field causes HINCRBY error = C [OK]

Hint: HINCRBY only works on numeric fields, not strings [OK]

Common Mistakes:

• Assuming HINCRBY creates or converts strings automatically
• Thinking key absence causes this error
• Believing increment must be string type

5. You have a Redis hash inventory with fields apples = 10 and oranges = 5. You want to add 3 apples and subtract 2 oranges using HINCRBY commands. Which sequence of commands correctly updates the inventory?

hard

A. HINCRBY inventory apples 3HINCRBY inventory oranges -2

B. HINCRBY inventory apples -3HINCRBY inventory oranges 2

C. HINCRBY inventory apples 3HINCRBY inventory oranges 2

D. HINCRBY inventory apples -3HINCRBY inventory oranges -2

Solution

1. Step 1: Identify the required changes

   We want to add 3 to apples and subtract 2 from oranges.

2. Step 2: Match increments with commands

   Adding 3 means increment by 3; subtracting 2 means increment by -2.

3. Step 3: Verify command sequence

   HINCRBY inventory apples 3
   HINCRBY inventory oranges -2 correctly uses HINCRBY inventory apples 3 and HINCRBY inventory oranges -2.

4. Final Answer:

   HINCRBY inventory apples 3
   HINCRBY inventory oranges -2 -> Option A

5. Quick Check:

   Add positive, subtract negative with HINCRBY = A [OK]

Hint: Use positive to add, negative to subtract with HINCRBY [OK]

Common Mistakes:

• Using negative to add or positive to subtract incorrectly
• Mixing up fields and increments
• Assuming HINCRBY can subtract by positive number