String Functions

Real-world text data is messy — inconsistent casing, extra whitespace, names that need combining. String functions clean and transform text directly in SQL.

Concatenation

-- ANSI standard (works in PostgreSQL, SQLite, SQL Server 2012+)
SELECT first_name || ' ' || last_name AS full_name FROM employees;

-- MySQL (also works in SQL Server)
SELECT CONCAT(first_name, ' ', last_name) AS full_name FROM employees;

Changing case

SELECT UPPER(first_name), LOWER(last_name) FROM employees;

Trimming whitespace

SELECT TRIM('  padded value  ') AS cleaned;
SELECT LTRIM('  left padded');
SELECT RTRIM('right padded  ');

Length

SELECT product_name, LENGTH(product_name) AS name_length FROM products;

SQL Server uses LEN() instead of LENGTH().

Substrings

-- First 3 characters
SELECT SUBSTRING(product_name, 1, 3) FROM products;

SQLite uses SUBSTR(); the rest generally accept both SUBSTR and SUBSTRING.

Replacing text

SELECT REPLACE(email, '@csa-demo.local', '@company.com') FROM employees;

Finding position

-- Position of '@' within the email (1-based)
SELECT email, INSTR(email, '@') FROM employees; -- SQLite / MySQL
SELECT email, POSITION('@' IN email) FROM employees; -- PostgreSQL
SELECT email, CHARINDEX('@', email) FROM employees; -- SQL Server

Putting it together

SELECT
  UPPER(TRIM(first_name)) || ' ' || UPPER(TRIM(last_name)) AS display_name,
  LENGTH(first_name) AS first_name_length
FROM employees
WHERE first_name LIKE 'A%';

Open the Code Playground, pick any SQL engine (SQLite, PostgreSQL, MySQL, or SQL Server), and paste these queries in directly — the practice database above is already loaded for you, every time.

-- A ready-to-query practice database is loaded automatically before every run —
-- no CREATE TABLE needed. Available tables:
--   departments  (id, name, location)
--   employees    (id, first_name, last_name, email, department_id, job_title, salary, hire_date, manager_id)
--   customers    (id, customer_name, city, country, signup_date)
--   products     (id, product_name, category, price, stock_quantity)
--   orders       (id, customer_id, employee_id, order_date, status)
--   order_items  (id, order_id, product_id, quantity, unit_price)

SELECT * FROM employees WHERE department_id = 1;