CLASS XII MySQL String Functions

In Class XII CBSE Computer Science (Code 083) and Informatics Practices (Code 065), String (Text) Functions are a vital part of the MySQL syllabus. These are Single Row Functions that operate on a single value and return a single value.

Core MySQL String Functions (CBSE Syllabus)

1. Case Conversion Functions

These functions change the letter case of the input string.

Function	Purpose	Example	Result
`LOWER()` / `LCASE()`	Converts characters to lowercase.	SELECT LOWER('CBSE');	'cbse'
`UPPER()` / `UCASE()`	Converts characters to uppercase.	SELECT UPPER('class 12');	'CLASS 12'

2. Length & Position Functions

Used to measure strings or find the location of specific characters.

Function	Purpose	Example	Result
LENGTH()	Returns the number of characters in a string.	SELECT LENGTH('Informatics');	11
INSTR()	Returns the position of the first occurrence of a substring.	SELECT INSTR('Computer', 'mp');	3

3. Substring Extraction Functions

Used to pull out a specific portion of a string. Note: In MySQL, the index starts at 1.

Function	Purpose	Example	Result
LEFT()	Returns the leftmost 'n' characters.	SELECT LEFT('Science', 3);	'Sci'
RIGHT()	Returns the rightmost 'n' characters.	SELECT RIGHT('Science', 3);	'nce'
`SUBSTR()` / `MID()`	Extracts a string from a start position for 'n' characters.	SELECT SUBSTR('Database', 3, 4);	'taba'

4. Trimming Functions

Used to remove unwanted leading or trailing spaces.

LTRIM(str): Removes leading spaces (left side).
- Example: SELECT LTRIM(' Hello'); $\rightarrow$ 'Hello'
RTRIM(str): Removes trailing spaces (right side).
- Example: SELECT RTRIM('Hello '); $\rightarrow$ 'Hello'
TRIM(str): Removes spaces from both sides.
- Example: SELECT TRIM(' Hello '); $\rightarrow$ 'Hello'

Important Board Exam Concepts

A. Nested String Functions

The board often asks for the output of functions combined together. Solve them from the inside out.

Example:

SELECT UPPER(SUBSTR('informaticspractices', 1, 11));

SUBSTR(..., 1, 11) $\rightarrow$ 'informatics'
UPPER('informatics') $\rightarrow$ 'INFORMATICS'

B. String Indexing

Unlike Python (where index starts at 0), MySQL indexing starts at 1.

SELECT SUBSTR('HELLO', 1, 1); $\rightarrow$ 'H' (Not 'E')

Solved Board-Style Questions

Q1. Write the output of:

SELECT RIGHT(LTRIM(' PYTHON'), 3);

Step 1: LTRIM removes spaces $\rightarrow$ 'PYTHON'
Step 2: RIGHT(..., 3) $\rightarrow$ 'HON'

Q2. Write a SQL command to display the first 3 characters of the column StudentName.

Ans: SELECT LEFT(StudentName, 3) FROM Students;

Q3. What is the difference between LENGTH() and INSTR()?

Ans: LENGTH() returns the total number of characters in a string, whereas INSTR() returns the numerical position of a specific substring within a string.