SET and GET commands in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the Redis SET command do?

The SET command stores a value with a specified key in Redis. It saves data so you can get it later.

beginner

How do you retrieve a value stored in Redis?

Use the GET command with the key to get the stored value back.

beginner

What happens if you use GET on a key that does not exist?

Redis returns null (or nil) because there is no value stored for that key.

intermediate

Can the SET command overwrite an existing key's value?

Yes, SET replaces the old value with the new one if the key already exists.

beginner

What is a simple example of using SET and GET in Redis?

Example:
SET name "Alice"
Then:
GET name
Returns: Alice

What does the Redis SET command require as input?

A Only a value

B A key and a value

C Only a key

D A key, value, and expiration time

The SET command needs both a key and a value to store data.

What will GET mykey return if mykey does not exist?

A An error message

B An empty string

C The string "null"

D A null or nil value

Redis returns a null or nil value when the key is not found.

If you run SET user "Bob" and then SET user "Alice", what will GET user return?

A "Alice"

B "Bob"

C An error

D Both values

The second SET overwrites the first value, so GET user returns "Alice".

Which command retrieves the value of a key in Redis?

A DEL

B SET

C GET

D EXPIRE

GET is used to retrieve the value stored at a key.

What type of data structure do SET and GET commands work with in Redis?

A Strings

B Hashes

C Sets

D Lists

SET and GET work with string values stored by keys.

Explain how the Redis SET and GET commands work together to store and retrieve data.

Think about saving and looking up a label on a box.

Describe what happens if you try to get a key that was never set in Redis.

Imagine looking for a box label that is not there.

Practice

1. What does the Redis SET command do?

easy

A. Retrieves a value by key

B. Stores a value with a specified key

C. Deletes a key and its value

D. Lists all keys in the database

Solution

1. Step 1: Understand the purpose of SET

   The SET command in Redis is used to save or store a value associated with a key.

2. Step 2: Compare with other commands

   GET retrieves values, DEL deletes keys, and KEYS lists keys, so they are not correct here.

3. Final Answer:

   Stores a value with a specified key -> Option B

4. Quick Check:

   SET saves data = A [OK]

Hint: SET saves data by key, GET fetches it [OK]

Common Mistakes:

• Confusing SET with GET
• Thinking SET deletes data
• Mixing SET with key listing

2. Which of the following is the correct syntax to store the value "hello" with the key "greeting" in Redis?

easy

A. SET greeting hello

B. GET greeting hello

C. SET "greeting" "hello"

D. SET greeting, hello

Solution

1. Step 1: Recall Redis SET syntax

   The correct syntax is SET key value without commas or quotes unless the shell requires them.

2. Step 2: Analyze options

   SET greeting hello matches the correct syntax. GET greeting hello uses GET which is wrong. SET "greeting" "hello" uses quotes unnecessarily. SET greeting, hello uses a comma which is invalid.

3. Final Answer:

   SET greeting hello -> Option A

4. Quick Check:

   SET key value no commas [OK]

Hint: Use SET key value without commas or quotes [OK]

Common Mistakes:

• Using GET instead of SET
• Adding commas between arguments
• Unnecessary quotes around key/value

3. Given the following Redis commands executed in order:

SET color blue
GET color
SET color red
GET color

What will be the output of the two GET commands?

medium

A. "blue" and then "red"

B. "red" and then "blue"

C. "blue" and then "blue"

D. nil and then "red"

Solution

1. Step 1: Analyze the first SET and GET

   The first SET color blue stores "blue". The first GET color returns "blue".

2. Step 2: Analyze the second SET and GET

   The second SET color red overwrites the value with "red". The second GET color returns "red".

3. Final Answer:

   "blue" and then "red" -> Option A

4. Quick Check:

   SET overwrites value, GET returns current value [OK]

Hint: SET overwrites; GET returns latest value [OK]

Common Mistakes:

• Assuming GET returns old value
• Thinking SET appends values
• Expecting nil on first GET

4. You run the command GET username but get a nil response. Which of the following could fix this issue?

medium

A. Run GET username again immediately

B. Use DEL username before GET

C. Restart the Redis server

D. Run SET username "guest" before GET

Solution

1. Step 1: Understand nil response from GET

   Nil means the key "username" does not exist or has no value stored.

2. Step 2: Fix by setting a value

   To get a value, you must first store it using SET username "guest". Other options do not create the key.

3. Final Answer:

   Run SET username "guest" before GET -> Option D

4. Quick Check:

   Nil means no key; SET creates it [OK]

Hint: Nil means missing key; SET it first [OK]

Common Mistakes:

• Retrying GET without SET
• Deleting key before GET
• Restarting server unnecessarily

5. You want to store a user's session token in Redis with key "session:123" and value "abc123token". Which sequence of commands correctly stores and retrieves this token?

hard

A. SET session:123 abc123token
DEL session:123
GET session:123

B. GET session:123
SET session:123 abc123token

C. SET session:123 abc123token
GET session:123

D. SET "session:123" "abc123token"
DEL session:123
GET session:123

Solution

1. Step 1: Store the session token

   Use SET session:123 abc123token to save the token under the key.

2. Step 2: Retrieve the stored token

   Use GET session:123 to fetch the token value.

3. Step 3: Analyze other options

   GET session:123 SET session:123 abc123token tries to GET before SET, so returns nil. Options A and C delete the key before GET, so GET returns nil.

4. Final Answer:

   SET session:123 abc123token GET session:123 -> Option C

5. Quick Check:

   SET then GET returns stored value [OK]

Hint: Always SET before GET to retrieve stored data [OK]

Common Mistakes:

• GET before SET returns nil
• Deleting key before GET
• Using quotes unnecessarily