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String Functions

Introduction

String functions in SQL are used to manipulate and perform operations on character strings. This section will cover common string functions, their syntax, and examples of how to use them.

CONCAT Function

The CONCAT function is used to concatenate two or more strings together.

CONCAT(string1, string2, ...);

Example

Concatenate first name and last name into a full name:

SELECT CONCAT(firstname, ' ', lastname) AS full_name
FROM employees;

SUBSTRING Function

The SUBSTRING function extracts a substring from a string.

SUBSTRING(string, start_position,length);
  • string: The source string from which the substring will be extracted.
  • start_position: The starting position from which to extract the substring.
  • length: Optional. The number of characters to extract.

Example

Extract the first three characters of the product name:

SELECT SUBSTRING(productname, 1,3) AS short_name
FROM products;

UPPER and LOWER Functions

The UPPER function converts a string to uppercase, while the LOWER function converts a string to lowercase.

UPPER(string);
LOWER(string);

Example

Convert the last name to uppercase and first name to lowercase:

SELECT UPPER(lastname) AS last_name_upper, LOWER(firstname) AS first_name_lower
FROM employees;

LENGTH Function

The LENGTH function returns the length of a string.

LENGTH(string);

Example

Calculate the length of the email addresses:

SELECT email, LENGTH(email) AS email_length
FROM customers;

TRIM Function

The TRIM function removes leading and trailing spaces from a string.

TRIM([LEADING | TRAILING | BOTH] trim_character FROM string);

Example

Remove leading and trailing spaces from the address:

SELECT TRIM(address) AS cleaned_address
FROM customers;

REPLACE Function

The REPLACE function replaces occurrences of a specified string with another string.

REPLACE(string, old_substring, new_substring);

Example

Replace 'Street' with 'St.' in the address:

SELECT REPLACE(address, 'Street', 'St.') AS modified_address
FROM customers;

Practice Exercises

  • Select only the first character from all employees first name
  • Using the results from the exercise above concatenate the first letter with the lastname, this must have a space inbetween.

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