TYPE command for key type check in Redis - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ query_result

intermediate

Check the type of a string key

Given a Redis database where the key user:1000 holds the value "Alice" as a string, what will be the output of the command TYPE user:1000?

Redis

TYPE user:1000

A "list"

B "string"

C "set"

D "none"

💡 Hint

Remember that Redis stores simple text values as strings.

The TYPE command returns the data type of the key. Since user:1000 holds a string value, the output is "string".

❓ query_result

intermediate

Check type of a non-existing key

What will the command TYPE session:9999 return if the key session:9999 does not exist in the Redis database?

Redis

TYPE session:9999

A "empty"

B "null"

C "error"

D "none"

💡 Hint

Think about what Redis returns when a key is missing.

Redis returns "none" when the key does not exist.

❓ query_result

advanced

Identify the type of a sorted set key

If the key leaderboard contains a sorted set of player scores, what will TYPE leaderboard return?

Redis

TYPE leaderboard

A "zset"

B "set"

C "hash"

D "list"

💡 Hint

Sorted sets have a special type name in Redis.

Redis uses "zset" to represent sorted sets.

❓ query_result

advanced

Detect type of a hash key

What is the output of TYPE user:profile if user:profile is a hash storing user attributes?

Redis

TYPE user:profile

A "hash"

B "string"

C "list"

D "none"

💡 Hint

Hashes store field-value pairs in Redis.

The TYPE command returns "hash" for keys storing hashes.

🧠 Conceptual

expert

Understanding TYPE command behavior with expired keys

If a key temp:data is set with an expiration and expires before the TYPE temp:data command is run, what will the TYPE command return?

A "expired"

B "string"

C "none"

D "error"

💡 Hint

Expired keys are automatically removed from Redis.

Once a key expires, it is deleted and no longer exists, so TYPE returns "none".

Practice

1. What does the Redis TYPE command do?

easy

A. It deletes the key from the database.

B. It sets a new value for the key.

C. It returns the data type stored at a given key.

D. It lists all keys in the database.

Solution

1. Step 1: Understand the purpose of TYPE command

   The TYPE command is used to find out what kind of data is stored at a specific key in Redis.

2. Step 2: Compare with other commands

   Unlike commands that delete, set, or list keys, TYPE only returns the data type like string, list, or none.

3. Final Answer:

   It returns the data type stored at a given key. -> Option C

4. Quick Check:

   TYPE command = returns key data type [OK]

Hint: TYPE shows key's data type before operations [OK]

Common Mistakes:

• Confusing TYPE with DEL command
• Thinking TYPE changes data
• Assuming TYPE lists keys

2. Which of the following is the correct syntax to check the type of a key named user:1 in Redis?

easy

A. TYPE user:1

B. GET TYPE user:1

C. CHECKTYPE user:1

D. TYPE(key=user:1)

Solution

1. Step 1: Recall Redis TYPE command syntax

   The correct syntax is simply TYPE keyname, so for key user:1, it is TYPE user:1.

2. Step 2: Identify incorrect syntax options

   Options B, C, and D use invalid commands or formats not supported by Redis.

3. Final Answer:

   TYPE user:1 -> Option A

4. Quick Check:

   Correct syntax = TYPE keyname [OK]

Hint: Use TYPE followed by key name directly [OK]

Common Mistakes:

• Adding extra keywords like GET or CHECKTYPE
• Using parentheses or wrong command names
• Confusing with other Redis commands

3. Given these Redis commands executed in order:

SET name "Alice"
LPUSH colors "red"
SADD tags "new"
TYPE name
TYPE colors
TYPE tags
TYPE age

What will be the output of the last four TYPE commands respectively?

medium

A. ["none", "list", "set", "string"]

B. ["string", "set", "list", "none"]

C. ["list", "string", "set", "none"]

D. ["string", "list", "set", "none"]

Solution

1. Step 1: Identify data types set by commands

   SET name "Alice" creates a string key.
   LPUSH colors "red" creates a list.
   SADD tags "new" creates a set.
   age key is not set, so it does not exist.

2. Step 2: Match TYPE outputs to keys

   TYPE name returns "string".
   TYPE colors returns "list".
   TYPE tags returns "set".
   TYPE age returns "none" because key does not exist.

3. Final Answer:

   ["string", "list", "set", "none"] -> Option D

4. Quick Check:

   TYPE outputs = [string, list, set, none] [OK]

Hint: Match commands to Redis data types exactly [OK]

Common Mistakes:

• Mixing up list and set types
• Assuming missing keys return error instead of none
• Confusing string with other types

4. You run the command TYPE mykey but get an unexpected output. Which of these is a likely cause?

medium

A. You used TYPE with wrong syntax like TYPE(mykey).

B. You tried to use TYPE on a key with a value longer than 100 characters.

C. The Redis server is down.

D. The key mykey does not exist in the database.

Solution

1. Step 1: Check command syntax

   Redis TYPE command requires syntax: TYPE keyname without parentheses. Using TYPE(mykey) causes syntax error or unexpected output.

2. Step 2: Evaluate other options

   If key does not exist, TYPE returns "none" (not unexpected). Server down causes connection errors, not TYPE output. Value length does not affect TYPE command.

3. Final Answer:

   You used TYPE with wrong syntax like TYPE(mykey). -> Option A

4. Quick Check:

   Correct syntax needed = TYPE keyname [OK]

Hint: Avoid parentheses in TYPE command syntax [OK]

Common Mistakes:

• Using parentheses with TYPE command
• Confusing missing key output with errors
• Blaming value size for TYPE issues

5. You want to write a Redis script that checks the type of a key and performs different actions based on it. Which sequence correctly uses the TYPE command and handles the case where the key does not exist?

hard

A. Use EXISTS key and if true, assume type is "string".

B. Use TYPE key to get type, then check if result is "none" before proceeding.

C. Use GET key and if it returns null, assume type is "none".

D. Use TYPE key and ignore the "none" result since it means key is empty.

Solution

1. Step 1: Use TYPE command to get key type

   The TYPE command returns the exact data type or "none" if the key does not exist.

2. Step 2: Check for "none" result before actions

   Before performing actions, check if TYPE returned "none" to handle missing keys properly.

3. Final Answer:

   Use TYPE key to get type, then check if result is "none" before proceeding. -> Option B

4. Quick Check:

   Check TYPE result for "none" to handle missing keys [OK]

Hint: Always check TYPE output for "none" before actions [OK]

Common Mistakes:

• Assuming GET null means type is string
• Assuming EXISTS means type is string
• Ignoring "none" type results