TYPE command for key type check in Redis - Step-by-Step Execution

Concept Flow - TYPE command for key type check

Start

↓

Input key name

↓

Check if key exists

↓

Get key type

↓

Return type string

↓

End

The TYPE command checks if a key exists and returns its data type or 'none' if it does not exist.

Execution Sample

Redis

TYPE mykey
TYPE unknownkey

Check the data type of 'mykey' and 'unknownkey' keys in Redis.

Execution Table

Step	Command	Key	Key Exists?	Returned Type
1	TYPE mykey	mykey	Yes	string
2	TYPE unknownkey	unknownkey	No	none

💡 Execution stops after checking all requested keys.

Variable Tracker

Variable	Start	After Step 1	After Step 2
key	undefined	mykey	unknownkey
key_exists	undefined	true	false
type_result	undefined	string	none

Key Moments - 2 Insights

Why does TYPE return 'none' for some keys?

TYPE returns 'none' when the key does not exist in the database, as shown in step 2 of the execution_table.

Can TYPE return types other than 'string' or 'none'?

Yes, TYPE can return types like 'list', 'set', 'hash', or 'zset' depending on the stored data type, but in this example only 'string' and 'none' appear.

Visual Quiz - 3 Questions

Look at the execution_table, what is the returned type for 'mykey' at step 1?

A list

B none

C string

D hash

💡 Hint

Check the 'Returned Type' column in row 1 of the execution_table.

At which step does the TYPE command return 'none'?

A Step 1

B Step 2

C Both steps

D None

💡 Hint

Look at the 'Returned Type' column for each step in the execution_table.

If the key 'mykey' was deleted before step 1, what would TYPE return?

A none

B set

C string

D error

💡 Hint

Refer to the behavior shown in step 2 where the key does not exist.

Concept Snapshot

TYPE key
Returns the data type of the key.
If key exists, returns type like string, list, set, hash, zset.
If key does not exist, returns 'none'.
Useful to check key type before operations.

Full Transcript

The TYPE command in Redis checks the data type of a given key. First, it checks if the key exists. If it does, it returns the type as a string such as 'string', 'list', or 'hash'. If the key does not exist, it returns 'none'. For example, TYPE mykey returned 'string' because 'mykey' exists and holds a string. TYPE unknownkey returned 'none' because that key does not exist. This helps avoid errors by confirming the key type before performing operations.

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