What are MySQL's built-in string functions and how to use them?
Aug 03, 2025 am 01:07 AM
MySQL provides a comprehensive set of string functions for efficient text manipulation, 1. CONCAT() and CONCAT_WS() combine strings with or without a separator, 2. CHAR_LENGTH() and LENGTH() return character and byte counts respectively, while UPPER(), LOWER() change case, 3. SUBSTRING(), LEFT(), and RIGHT() extract parts of strings, 4. LOCATE() and INSTR() find substring positions, 5. REPLACE() substitutes text and TRIM() removes unwanted characters from ends, 6. LPAD() and RPAD() pad strings to specified lengths, 7. REVERSE() reverses character order and REPEAT() duplicates strings, 8. STRCMP() compares strings, while LIKE and REGEXP enable pattern matching, and these functions can be combined for powerful text processing directly in SQL queries, reducing the need for application-level manipulation.
MySQL provides a rich set of built-in string functions that allow you to manipulate and work with text data efficiently. These functions are useful for formatting, searching, extracting, and transforming string values in your queries. Below are some of the most commonly used MySQL string functions, along with explanations and examples.
1. String Concatenation: CONCAT() and CONCAT_WS()
-
CONCAT(str1, str2, ...)
Combines two or more strings into one.SELECT CONCAT('Hello', ' ', 'World'); -- Result: 'Hello World' CONCAT_WS(separator, str1, str2, ...)
Concatenates strings with a specified separator (WS = With Separator).
SELECT CONCAT_WS('-', '2024', '04', '01'); -- Result: '2024-04-01'
2. String Length and Case Conversion
CHAR_LENGTH(str)orLENGTH(str)CHAR_LENGTH()returns the number of characters.LENGTH()returns the number of bytes (important for multi-byte characters like UTF-8).
SELECT CHAR_LENGTH('Hello'); -- 5 SELECT LENGTH('Hello'); -- 5UPPER(str)/UCASE(str)andLOWER(str)/LCASE(str)
Convert strings to uppercase or lowercase.SELECT UPPER('hello'); -- 'HELLO' SELECT LOWER('WORLD'); -- 'world'
3. Substring Extraction: SUBSTRING(), LEFT(), RIGHT()
SUBSTRING(str, pos, len)orSUBSTR()
Extracts a substring starting at positionposwith lengthlen. Position starts at 1.SELECT SUBSTRING('MySQL Tutorial', 1, 5); -- 'MySQL' SELECT SUBSTRING('MySQL Tutorial', -9, 8); -- 'Tutorial' (from end)LEFT(str, n)andRIGHT(str, n)
Returns the firstncharacters from the left or right.SELECT LEFT('abcdef', 3); -- 'abc' SELECT RIGHT('abcdef', 3); -- 'def'
4. Finding Substrings: LOCATE() and INSTR()
LOCATE(substr, str, pos)
Returns the position of the first occurrence ofsubstrinstr, starting from optionalpos.SELECT LOCATE('SQL', 'MySQL Tutorial'); -- 3INSTR(str, substr)
Similar toLOCATE(), but no start position parameter.SELECT INSTR('MySQL', 'SQL'); -- 3
5. String Replacement and Removal
REPLACE(str, from_str, to_str)
Replaces all occurrences offrom_strwithto_str.SELECT REPLACE('Hello World', 'World', 'MySQL'); -- 'Hello MySQL'TRIM([LEADING|TRAILING|BOTH] [char] FROM str)
Removes leading, trailing, or both spaces (or specified characters).SELECT TRIM(' hello '); -- 'hello' SELECT TRIM(BOTH 'x' FROM 'xxhelloxx'); -- 'hello' SELECT LTRIM(' hello'); -- 'hello' (leading only) SELECT RTRIM('hello '); -- 'hello' (trailing only)
6. Padding and Formatting: LPAD() and RPAD()
LPAD(str, len, padstr)
Left-pads the string to a total length oflenusingpadstr.SELECT LPAD('123', 6, '0'); -- '000123'RPAD(str, len, padstr)
Right-pads the string.SELECT RPAD('123', 6, '0'); -- '123000'
7. Reverse and Repeat
REVERSE(str)
Reverses the characters in the string.SELECT REVERSE('abc'); -- 'cba'REPEAT(str, count)
Repeats the stringcounttimes.SELECT REPEAT('Hi', 3); -- 'HiHiHi'
8. String Comparison and Pattern Matching
STRCMP(str1, str2)
Compares two strings:- Returns 0 if equal
- -1 if
str1 < str2 - 1 if
str1 > str2
SELECT STRCMP('abc', 'abc'); -- 0 SELECT STRCMP('abc', 'def'); -- -1LIKEandREGEXP/RLIKE
Not functions per se, but useful for pattern matching inWHEREclauses.SELECT 'apple' LIKE 'a%'; -- 1 (true) SELECT 'apple' REGEXP '^a'; -- 1 (true)
Practical Example: Formatting Names
Suppose you have a table users with first_name and last_name, and you want to generate a full name in title case and extract domain from email.
SELECT CONCAT(UPPER(LEFT(first_name, 1)), LOWER(SUBSTRING(first_name, 2))) AS FirstName, CONCAT(UPPER(LEFT(last_name, 1)), LOWER(SUBSTRING(last_name, 2))) AS LastName, SUBSTRING_INDEX(email, '@', -1) AS domain FROM users;
This capitalizes the first letter of each name and extracts the email domain.
These functions can be combined in powerful ways to clean, format, and analyze text data directly within SQL queries. Knowing when and how to use them helps reduce post-processing in application code.
Basically, just pick the right function based on whether you're extracting, searching, replacing, or formatting strings.
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