LENGTH and CHAR_LENGTH in MySQL

Introduction

We use LENGTH and CHAR_LENGTH to find out how long a piece of text is. LENGTH counts bytes, CHAR_LENGTH counts characters.

When you want to know how many characters a name or word has.

When you need to check the size of text data before saving it.

When you want to compare text lengths in different languages.

When you want to count characters in a message or comment.

When you want to find out if a text is empty or too long.

Syntax

MySQL

LENGTH(string)
CHAR_LENGTH(string)

LENGTH returns the number of bytes used by the string.

CHAR_LENGTH returns the number of characters in the string.

Examples

Returns 5 because 'hello' has 5 bytes (1 byte per character).

MySQL

SELECT LENGTH('hello');

Returns 5 because 'hello' has 5 characters.

MySQL

SELECT CHAR_LENGTH('hello');

Returns 7 because 'ñ' and 'ú' use 2 bytes each in UTF-8.

MySQL

SELECT LENGTH('ñandú');

Returns 5 because there are 5 characters in the word.

MySQL

SELECT CHAR_LENGTH('ñandú');

Sample Program

This query shows the difference between LENGTH and CHAR_LENGTH for the word 'café'.

MySQL

SELECT LENGTH('café') AS length_bytes, CHAR_LENGTH('café') AS length_chars;

Important Notes

For simple English letters, LENGTH and CHAR_LENGTH usually return the same number.

For special characters or accents, LENGTH counts bytes, so it can be higher than CHAR_LENGTH.

Use CHAR_LENGTH when you want to count characters, not bytes.

Summary

LENGTH counts bytes in a string.

CHAR_LENGTH counts characters in a string.

Use these functions to check text size or length in your database.

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