DataBolt

All Lessons

Introduction to SQL

SQL Lesson 1: Your Sample Database

SQL Lesson 2: SELECT — Reading data

SQL Lesson 3: WHERE — Filtering rows

SQL Lesson 4: AND, OR, NOT

SQL Lesson 5: BETWEEN, IN, LIKE

SQL Lesson 6: NULL — The Mystery Value

SQL Lesson 7: ORDER BY

SQL Lesson 8: LIMIT & OFFSET

SQL Lesson 9: Aggregate Functions

SQL Lesson 10: GROUP BY

SQL Lesson 11: HAVING

SQL Lesson 12: INNER JOINs

SQL Lesson 13: LEFT JOINs

SQL Lesson 14: RIGHT JOINs

SQL Lesson 15: SELF JOINs

SQL Lesson 16: UNION JOINs

SQL Lesson 17: Joining Multiple Tables

SQL Lesson 18: Subqueries

SQL Lesson 19: CTEs (WITH)

SQL Lesson 20: CASE Statements

SQL Lesson 21: Window Functions

SQL Lesson 22: String Functions

SQL Lesson 23: Date & Time Functions

SQL Lesson 24: INSERT, UPDATE, DELETE

SQL Lesson 25: CREATE TABLE & DDL

SQL Lesson 26: Indexes & Performance

SQL Lesson 27: Transactions & ACID

SQL Lesson 28: SQL Execution Order

SQL Lesson 29: 50 Practice Problems

CHAPTER 23

String Functions

Manipulating and transforming text data.

IN THIS CHAPTER

UPPER, LOWER, TRIM — basic cleanup
CONCAT — combining strings
SUBSTRING, LEFT, RIGHT — extracting parts
REPLACE, INSTR — search and replace

Function	What It Does	Example → Output
UPPER(str)	Convert to uppercase	UPPER('sql book') → 'SQL BOOK'
LOWER(str)	Convert to lowercase	LOWER('SQL') → 'sql'
TRIM(str)	Remove leading + trailing spaces	TRIM(' hi ') → 'hi'
LENGTH(str)	Number of characters	LENGTH('Arjun') → 5
CONCAT(s1,s2,...)	Join strings	CONCAT('Hello','SQL') → 'Hello SQL'
LEFT(str,n)	First n characters	LEFT('Bangalore',4) → 'Bang'
RIGHT(str,n)	Last n characters	RIGHT('Bangalore',4) → 'lore'
SUBSTRING(s,pos,n)	Extract n chars from position	SUBSTRING('Hyderabad',2,5) → 'yderi'
REPLACE(s,old,new)	Replace all occurrences	REPLACE('SQL is hard','hard','easy')
INSTR(str,sub)	Position of substring	INSTR('Hyderabad','bad') → 7

Real Examples

Full display string with city

SELECT CONCAT(name, ' — ', city, ', ', country) AS profile
FROM customers;

Included Tables in Exercise

Table: Employees

emp_id	name	department	salary	manager_id	hire_date
1	Arjun	IT	85000	NULL	2020-06-15
2	Priya	IT	72000	1	2021-03-10
3	Rahul	Sales	55000	5	2022-01-20
4	Sneha	HR	60000	5	2021-07-08
5	Vikram	Sales	90000	NULL	2019-11-01
6	Divya	IT	68000	1	2023-02-14
7	Kiran	HR	58000	4	2022-08-30
8	Meera	Sales	62000	5	2023-05-12

Table: Customers

customer_id	name	city	country
1	Ananya	Hyderabad	India
2	Rohan	Bangalore	India
3	Sam	Mumbai	India
4	Lisa	London	UK
5	Ravi	Delhi	India

Exercise 👇

Exercise:

Tasks

1.👉Convert all employee names to uppercase.

2.Convert all customer names to lowercase.

3.Find the length of each employee's name.

4.Combine employee name and department into a single column.

5.Extract first 3 characters of each customer's city.

Stuck? Read this task's