LENGTH and CHAR_LENGTH in MySQL - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to get the byte length of the string 'hello'.

MySQL

SELECT [1]('hello') AS length_bytes;

Drag options to blanks, or click blank then click option'

ACHAR_LENGTH

BLENGTH

CLEN

DSIZE

Attempts:

3 left

💡 Hint

Common Mistakes

Using CHAR_LENGTH instead of LENGTH for byte count.

Using LEN which is not a MySQL function.

The LENGTH function returns the number of bytes in the string.

2fill in blank

medium

Complete the code to get the number of characters in the string 'café'.

MySQL

SELECT [1]('café') AS char_count;

Drag options to blanks, or click blank then click option'

ALEN

BLENGTH

CSIZE

DCHAR_LENGTH

Attempts:

3 left

💡 Hint

Common Mistakes

Using LENGTH which counts bytes, not characters.

Using LEN which is not valid in MySQL.

The CHAR_LENGTH function returns the number of characters, which is 4 for 'café'.

3fill in blank

hard

Fix the error in the code to correctly get the character count of 'naïve'.

MySQL

SELECT [1]('naïve') AS char_count;

Drag options to blanks, or click blank then click option'

ACHAR_LENGTH

BLENGTH

CLEN

DSIZE

Attempts:

3 left

💡 Hint

Common Mistakes

Using LENGTH which counts bytes, leading to incorrect count.

Using LEN which causes syntax error.

CHAR_LENGTH correctly returns the number of characters, including multibyte characters like 'ï'.

4fill in blank

hard

Fill both blanks to get the byte length and character length of 'résumé'.

MySQL

SELECT [1]('résumé') AS bytes, [2]('résumé') AS chars;

Drag options to blanks, or click blank then click option'

ALENGTH

BCHAR_LENGTH

CLEN

DSIZE

Attempts:

3 left

💡 Hint

Common Mistakes

Swapping LENGTH and CHAR_LENGTH.

Using LEN or SIZE which are invalid.

LENGTH returns bytes, CHAR_LENGTH returns characters.

5fill in blank

hard

Fill all three blanks to get the byte length, character length, and compare if they are equal for 'touché'.

MySQL

SELECT [1]('touché') AS bytes, [2]('touché') AS chars, ([1]('touché') [3] [2]('touché')) AS equal_lengths;

Drag options to blanks, or click blank then click option'

ALENGTH

BCHAR_LENGTH

C=

D==

Attempts:

3 left

💡 Hint

Common Mistakes

Using == which is invalid in SQL.

Mixing up LENGTH and CHAR_LENGTH.

LENGTH and CHAR_LENGTH get bytes and characters. Use = for comparison in SQL.

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