SQL Wildcards

In SQL, wildcards are special characters that can be used with the LIKE operator in the WHERE clause of a SELECT statement to match patterns in text.

The following are the commonly used wildcards in SQL:

1. % (percent sign) - Represents any number of characters, including none. For example, the following statement retrieves all employees whose first names start with "J":

SELECT * FROM employees WHERE first_name LIKE 'J%';

2. _ (underscore) - Represents a single character. For example, the following statement retrieves all employees whose first names have five letters, where the third letter is "a":

SELECT * FROM employees WHERE first_name LIKE '__a__';

3. [] (brackets) - Represents a single character within a range or a set. For example, the following statement retrieves all employees whose last names start with "B", "C", or "D":

SELECT * FROM employees WHERE last_name LIKE '[BCD]%';

4. [^] (caret) - Represents a single character not within a range or a set. For example, the following statement retrieves all employees whose last names do not start with "B", "C", or "D":

SELECT * FROM employees WHERE last_name LIKE '[^BCD]%';

Using wildcards can make your queries more flexible and powerful. However, it is important to use them carefully and to avoid using them too often, as they can significantly slow down the performance of your queries.