LIKE and ILIKE Clause in SQL

The LIKE and ILIKE clauses in SQL are used for pattern matching in string data.

• LIKE: Performs case-sensitive matching.

• ILIKE: Performs case-insensitive matching (commonly used in databases like PostgreSQL).

Key Points

1. Pattern Matching:
   Both LIKE and ILIKE use wildcard characters (% and _) to define patterns:

   • %: Matches zero or more characters.

   • _: Matches exactly one character.

2. Case Sensitivity:

   • LIKE is case-sensitive, meaning it distinguishes between uppercase and lowercase letters.

   • ILIKE is case-insensitive, meaning it treats uppercase and lowercase letters as the same.

Syntax

Basic Syntax

SELECT column1, column2, ...
FROM table_name
WHERE column_name [NOT] LIKE pattern;

Using ILIKE

SELECT column1, column2, ...
FROM table_name
WHERE column_name [NOT] ILIKE pattern;

Example

Using LIKE for Case-Sensitive Matching

SELECT first_name, last_name
FROM employees
WHERE first_name LIKE 'A%';

• Retrieves employees whose first_name starts with 'A'.

Using ILIKE for Case-Insensitive Matching

SELECT first_name, last_name
FROM employees
WHERE first_name ILIKE 'a%';

• Retrieves employees whose first_name starts with 'A' or 'a'.

Using _ for Single Character Matching

SELECT product_name
FROM products
WHERE product_name LIKE '_pple';

• Finds products like "Apple," "Xpple," etc., where the second to fifth characters match.

Using Wildcards in the Middle or End

SELECT email
FROM users
WHERE email LIKE '%@gmail.com';

• Retrieves all email addresses ending with "@gmail.com".

Using NOT LIKE

SELECT first_name, last_name
FROM employees
WHERE last_name NOT LIKE '%son';

• Finds employees whose last name does not end with 'son'.

When to Use LIKE and ILIKE

• Use LIKE for case-sensitive searches when precision matters.

• Use ILIKE for case-insensitive searches, especially in user-facing applications.

• Ideal for scenarios involving partial text search or pattern matching.

Note: The performance of LIKE and ILIKE can degrade for complex patterns or large datasets without proper indexing.