HINCRBY for numeric fields in Redis - Step-by-Step Execution

Concept Flow - HINCRBY for numeric fields

Start with hash key and field

↓

Check if field exists in hash?

No→Initialize field to 0

Yes↓

Get current numeric value

↓

Add increment to current value

↓

Update field with new value

↓

Return new value

↓

End

This flow shows how HINCRBY checks a field in a hash, initializes it if missing, increments its numeric value, updates the field, and returns the new value.

Execution Sample

Redis

HSET user:1 age 30
HINCRBY user:1 age 5
HINCRBY user:1 visits 1

This code sets 'age' to 30, increments 'age' by 5, and increments a new field 'visits' by 1 in the 'user:1' hash.

Execution Table

Step	Command	Field Exists?	Current Value	Increment	New Value	Action
1	HSET user:1 age 30	N/A	N/A	N/A	30	Set 'age' to 30
2	HINCRBY user:1 age 5	Yes	30	5	35	Increment 'age' by 5
3	HINCRBY user:1 visits 1	No	0 (init)	1	1	Initialize 'visits' to 0 and increment by 1

💡 All commands executed; final hash fields: age=35, visits=1

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
user:1.age	null	30	35	35
user:1.visits	null	null	null	1

Key Moments - 2 Insights

What happens if the field does not exist before HINCRBY?

If the field does not exist (see step 3 in execution_table), Redis treats its value as 0 before adding the increment, then sets the field to the new value.

Can HINCRBY increment non-numeric fields?

No, HINCRBY only works on numeric fields. If the field contains a non-numeric string, Redis returns an error (not shown here).

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'age' after step 2?

A 30

B 5

C 35

D null

💡 Hint

Check the 'New Value' column in row for step 2 in execution_table.

At which step does the 'visits' field get created and set?

A Step 1

B Step 3

C Step 2

D Never

💡 Hint

Look at the 'Field Exists?' and 'Action' columns for 'visits' in execution_table.

If we increment 'age' by -10 at step 2 instead of 5, what would be the new value?

A 20

B 40

C 35

D 30

💡 Hint

Subtract 10 from the initial 30 value shown in variable_tracker after step 1.

Concept Snapshot

HINCRBY key field increment
- Increments numeric field in a hash by increment
- If field missing, treats as 0 before increment
- Returns new value after increment
- Only works with numeric fields

Full Transcript

HINCRBY is a Redis command to increment a numeric field inside a hash. If the field does not exist, Redis treats it as zero before adding the increment. The command updates the field with the new value and returns it. For example, setting 'age' to 30, then incrementing by 5 results in 35. Incrementing a missing field like 'visits' by 1 initializes it to 1. This command only works on numeric fields; non-numeric fields cause errors.