Real-world data is messy. Users type their names in ALL CAPS, phone numbers come in five different formats, email addresses have trailing spaces, and city names are spelled three different ways. Before you can analyze or display that data meaningfully, you need to clean and reshape it — and SQL string functions are one of the most powerful tools in your toolkit for doing exactly that.

In this guide, we'll go beyond the basics. You'll see how string functions work together to solve real data problems — the kind that show up constantly in reporting pipelines, backend APIs, and data migrations.

The Sample Database

We'll use a realistic customers table throughout this article:

CREATE TABLE customers ( customer_id SERIAL PRIMARY KEY , first_name VARCHAR ( 100 ), last_name VARCHAR ( 100 ), email VARCHAR ( 255 ), phone VARCHAR ( 30 ), city VARCHAR ( 100 ), country_code CHAR ( 2 ) );

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And here's the kind of data you might find in it after a messy data…