LENGTH and CHAR_LENGTH in MySQL - Step-by-Step Execution

Concept Flow - LENGTH and CHAR_LENGTH

Input String

↓

Output: Byte Count

↓

Input String

↓

Output: Character Count

LENGTH counts bytes in a string, CHAR_LENGTH counts characters. For ASCII, both are same; for multibyte (e.g., UTF-8), LENGTH can be larger.

Execution Sample

MySQL

SELECT LENGTH('hello'), CHAR_LENGTH('hello');
SELECT LENGTH('café'), CHAR_LENGTH('café');

Shows difference between LENGTH and CHAR_LENGTH on ASCII and accented characters.

Execution Table

Step	Input String	Function	Result	Explanation
1	'hello'	LENGTH('hello')	5	Each ASCII character is 1 byte, total 5 bytes
2	'hello'	CHAR_LENGTH('hello')	5	5 characters in string
3	'café'	LENGTH('café')	5	é is 2 bytes in UTF-8, total bytes = 4 + 1 = 5
4	'café'	CHAR_LENGTH('café')	4	4 characters total, counting accented as one character

💡 All function calls complete, results show byte vs character counts

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	Final
Input String	''	'hello'	'hello'	'café'	'café'	'café'
LENGTH Result	null	5	5	5	5	5
CHAR_LENGTH Result	null	—	5	—	4	4

Key Moments - 2 Insights

Why does LENGTH('café') return 5 but CHAR_LENGTH('café') returns 4?

Because LENGTH counts bytes, and 'é' uses 2 bytes in UTF-8, so total bytes are 5. CHAR_LENGTH counts characters, so 'café' has 4 characters.

Are LENGTH and CHAR_LENGTH always the same?

No, they are the same only for single-byte character sets like ASCII. For multibyte characters, LENGTH counts bytes, CHAR_LENGTH counts characters.

Visual Quiz - 3 Questions

Look at the execution table, what is the LENGTH('hello') result at step 1?

A 6

B 5

C 4

D 1

💡 Hint

Check the 'Result' column in row with Step 1 in execution_table

At which step does CHAR_LENGTH return 4?

A Step 4

B Step 2

C Step 3

D Step 1

💡 Hint

Look at the 'Function' and 'Result' columns in execution_table rows

If the input string was only ASCII characters, how would LENGTH and CHAR_LENGTH compare?

A LENGTH would be greater than CHAR_LENGTH

B CHAR_LENGTH would be greater than LENGTH

C Both would be equal

D Cannot determine

💡 Hint

Refer to the concept_flow description about ASCII characters

Concept Snapshot

LENGTH(string) returns number of bytes in string.
CHAR_LENGTH(string) returns number of characters.
For ASCII, both are equal.
For multibyte chars (e.g., UTF-8), LENGTH >= CHAR_LENGTH.
Use CHAR_LENGTH to count characters, LENGTH for bytes.

Full Transcript

This lesson shows how LENGTH and CHAR_LENGTH functions work in MySQL. LENGTH counts the number of bytes in a string, while CHAR_LENGTH counts the number of characters. For example, the string 'hello' has 5 bytes and 5 characters, so both functions return 5. But for 'café', LENGTH returns 5 because the accented 'é' uses 2 bytes in UTF-8 encoding, while CHAR_LENGTH returns 4 because there are 4 characters. This difference is important when working with multibyte character sets. Remember, LENGTH counts bytes, CHAR_LENGTH counts characters.

Practice

1. What does the MySQL function LENGTH() return when used on a string?

easy

A. The number of words in the string

B. The number of characters in the string

C. The number of lines in the string

D. The number of bytes in the string

Solution

1. Step 1: Understand LENGTH() function

   The LENGTH() function returns the number of bytes used by the string, not characters.

2. Step 2: Compare with CHAR_LENGTH()

   CHAR_LENGTH() counts characters, LENGTH() counts bytes, which can differ for multibyte characters.

3. Final Answer:

   The number of bytes in the string -> Option D

4. Quick Check:

   LENGTH() = bytes count [OK]

Hint: LENGTH counts bytes, CHAR_LENGTH counts characters [OK]

Common Mistakes:

• Confusing LENGTH() with CHAR_LENGTH()
• Assuming LENGTH() counts characters
• Thinking LENGTH() counts words

2. Which of the following is the correct syntax to get the number of characters in a string column named name in MySQL?

easy

A. SELECT LENGTH(name) FROM users;

B. SELECT CHAR_LENGTH(name) FROM users;

C. SELECT COUNT(name) FROM users;

D. SELECT SIZE(name) FROM users;

Solution

1. Step 1: Identify function for character count

   CHAR_LENGTH() returns the number of characters in a string, which is what we want.

2. Step 2: Check syntax correctness

   SELECT CHAR_LENGTH(name) FROM users; is valid syntax to get character count per row.

3. Final Answer:

   SELECT CHAR_LENGTH(name) FROM users; -> Option B

4. Quick Check:

   CHAR_LENGTH() counts characters [OK]

Hint: Use CHAR_LENGTH() to count characters, not LENGTH() [OK]

Common Mistakes:

• Using LENGTH() instead of CHAR_LENGTH() for characters
• Using COUNT() which counts rows, not string length
• Using non-existent SIZE() function

3. Given a table messages with a column text containing the value 'café', what will the query SELECT LENGTH(text), CHAR_LENGTH(text) FROM messages; return if the encoding is UTF-8?

medium

A. 5, 4

B. 4, 5

C. 4, 4

D. 5, 5

Solution

1. Step 1: Understand UTF-8 encoding for 'café'

   The character 'é' uses 2 bytes in UTF-8, so total bytes = 3 (c,a,f) + 2 (é) = 5 bytes.

2. Step 2: Count characters vs bytes

   CHAR_LENGTH counts characters: 'c','a','f','é' = 4 characters. LENGTH counts bytes = 5.

3. Final Answer:

   5, 4 -> Option A

4. Quick Check:

   LENGTH=5 bytes, CHAR_LENGTH=4 chars [OK]

Hint: UTF-8 chars may use multiple bytes; LENGTH > CHAR_LENGTH [OK]

Common Mistakes:

• Assuming LENGTH and CHAR_LENGTH return same value
• Ignoring multibyte characters in UTF-8
• Swapping LENGTH and CHAR_LENGTH results

4. You wrote the query SELECT LENGTH('hello'), CHAR_LENGTH('hello'); but got an error. What is the likely cause?

medium

A. No error; the query is valid and returns results

B. Missing FROM clause in the query

C. Incorrect function names, LENGTH and CHAR_LENGTH do not exist

D. Using single quotes instead of double quotes

Solution

1. Step 1: Check syntax of the query

   SELECT LENGTH('hello'), CHAR_LENGTH('hello'); is valid in MySQL and does not require FROM clause.

2. Step 2: Verify function existence and quotes

   LENGTH and CHAR_LENGTH are valid functions; single quotes are correct for string literals.

3. Final Answer:

   No error; the query is valid and returns results -> Option A

4. Quick Check:

   Query syntax is valid [OK]

Hint: MySQL allows SELECT without FROM for expressions [OK]

Common Mistakes:

• Thinking FROM clause is mandatory in all SELECT queries
• Confusing string quotes usage
• Assuming LENGTH or CHAR_LENGTH are invalid functions

5. You want to find all rows in a table users where the username column has exactly 5 characters, but some usernames contain multibyte UTF-8 characters. Which query correctly finds these rows?

hard

A. SELECT * FROM users WHERE LENGTH(username) = CHAR_LENGTH(username);

B. SELECT * FROM users WHERE LENGTH(username) = 5;

C. SELECT * FROM users WHERE CHAR_LENGTH(username) = 5;

D. SELECT * FROM users WHERE LENGTH(username) > 5;

Solution

1. Step 1: Understand difference between LENGTH and CHAR_LENGTH

   LENGTH counts bytes, which can be more than characters for multibyte UTF-8 chars.

2. Step 2: Choose function that counts characters

   CHAR_LENGTH counts characters correctly regardless of byte size, so use CHAR_LENGTH(username) = 5.

3. Final Answer:

   SELECT * FROM users WHERE CHAR_LENGTH(username) = 5; -> Option C

4. Quick Check:

   Use CHAR_LENGTH for character count in UTF-8 [OK]

Hint: Use CHAR_LENGTH to count characters, not bytes [OK]

Common Mistakes:

• Using LENGTH() which counts bytes, not characters
• Assuming byte count equals character count
• Using incorrect comparison operators