HSET and HGET for fields in Redis - Step-by-Step Execution

Concept Flow - HSET and HGET for fields

Start

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HSET key field value

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Store field-value in hash

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HGET key field

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Retrieve value for field

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Output value

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End

The flow shows setting a field-value pair in a hash with HSET, then retrieving the value with HGET.

Execution Sample

Redis

HSET user:1 name "Alice"
HSET user:1 age "30"
HGET user:1 name
HGET user:1 age

This code sets two fields 'name' and 'age' in the hash 'user:1' and then retrieves their values.

Execution Table

Step	Command	Action	Result	Hash State
1	HSET user:1 name "Alice"	Set field 'name' to 'Alice' in 'user:1'	1 (new field added)	{"name": "Alice"}
2	HSET user:1 age "30"	Set field 'age' to '30' in 'user:1'	1 (new field added)	{"name": "Alice", "age": "30"}
3	HGET user:1 name	Get value of field 'name' from 'user:1'	Alice	{"name": "Alice", "age": "30"}
4	HGET user:1 age	Get value of field 'age' from 'user:1'	30	{"name": "Alice", "age": "30"}
5	HGET user:1 email	Get value of non-existing field 'email'	nil (field does not exist)	{"name": "Alice", "age": "30"}

💡 No more commands; retrieval ends after last HGET.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
user:1 hash	{}	{"name": "Alice"}	{"name": "Alice", "age": "30"}	{"name": "Alice", "age": "30"}	{"name": "Alice", "age": "30"}	{"name": "Alice", "age": "30"}
name field value	nil	Alice	Alice	Alice	Alice	Alice
age field value	nil	nil	30	30	30	30
email field value	nil	nil	nil	nil	nil	nil

Key Moments - 2 Insights

Why does HGET return nil for a field that was never set?

Because the field does not exist in the hash, as shown in step 5 of the execution_table where HGET user:1 email returns nil.

What does the number returned by HSET mean?

It shows how many new fields were added. In steps 1 and 2, HSET returns 1 because each time a new field is added to the hash.

Visual Quiz - 3 Questions

Look at the execution_table, what is the hash state after step 2?

A {"name": "Alice"}

B {}

C {"name": "Alice", "age": "30"}

D {"age": "30"}

💡 Hint

Check the 'Hash State' column in row 2 of the execution_table.

At which step does HGET return nil?

A Step 5

B Step 4

C Step 3

D None

💡 Hint

Look at the 'Result' column for each HGET command in the execution_table.

If we run HSET user:1 name "Bob" after step 2, what will HGET user:1 name return?

A "Alice"

B "Bob"

C nil

D Error

💡 Hint

HSET updates the field value if it already exists, so the latest value is returned.

Concept Snapshot

HSET key field value - sets a field in a hash.
Returns 1 if new field added, 0 if updated.
HGET key field - gets the value of a field.
Returns nil if field does not exist.
Used to store and retrieve small sets of key-value pairs inside a Redis key.

Full Transcript

This visual execution shows how Redis commands HSET and HGET work with hash fields. First, HSET adds a field and value to a hash key. Each new field added returns 1. Then HGET retrieves the value for a given field. If the field exists, it returns the stored value. If the field does not exist, it returns nil. The hash state updates after each HSET, and remains unchanged after HGET. This helps store multiple related values under one key efficiently.