LENGTH and CHAR_LENGTH in MySQL - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the LENGTH() function return in MySQL?

LENGTH() returns the number of bytes used by a string, counting each byte including multi-byte characters.

beginner

What does the CHAR_LENGTH() function return in MySQL?

CHAR_LENGTH() returns the number of characters in a string, counting multi-byte characters as one character each.

intermediate

How do LENGTH() and CHAR_LENGTH() differ when used on a string with multi-byte characters?

LENGTH() counts bytes, so multi-byte characters count as multiple bytes. CHAR_LENGTH() counts characters, so each multi-byte character counts as one.

intermediate

Example: What is the result of LENGTH('café') and CHAR_LENGTH('café') if 'é' is a 2-byte character?

LENGTH('café') returns 5 (4 letters + 1 extra byte for 'é'), CHAR_LENGTH('café') returns 4 (four characters).

intermediate

Why is it important to use CHAR_LENGTH() instead of LENGTH() when counting characters in multi-byte strings?

Because LENGTH() counts bytes, it can overcount characters in multi-byte strings. CHAR_LENGTH() gives the true character count, which is often what you want.

What does LENGTH('hello') return in MySQL?

A 4

B 6

C 5

D 0

Each character in 'hello' is one byte, so LENGTH returns 5.

If 'é' is stored as 2 bytes, what does CHAR_LENGTH('café') return?

A 5

B 2

C 6

D 4

CHAR_LENGTH counts characters, so 'café' has 4 characters.

Which function counts bytes in a string in MySQL?

A CHAR_LENGTH()

B LENGTH()

C COUNT()

D SUBSTRING()

LENGTH() counts bytes, CHAR_LENGTH() counts characters.

What is the difference between LENGTH() and CHAR_LENGTH()?

A LENGTH counts bytes, CHAR_LENGTH counts characters

B LENGTH counts characters, CHAR_LENGTH counts bytes

C Both count characters

D Both count bytes

LENGTH counts bytes, CHAR_LENGTH counts characters.

Which function should you use to get the number of characters in a UTF-8 string?

A CHAR_LENGTH()

B LENGTH()

C ASCII()

D BIT_LENGTH()

CHAR_LENGTH() returns the number of characters, correctly handling multi-byte UTF-8 characters.

Explain the difference between LENGTH() and CHAR_LENGTH() in MySQL.

Think about how multi-byte characters are stored and counted.

When should you use CHAR_LENGTH() instead of LENGTH()?

Consider strings with accented or special 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