SQL wildcards are special characters that are used in SQL queries to represent one or more unspecified characters in search conditions, particularly within string matching operations. They are especially useful in conjunction with the LIKE operator, allowing developers to retrieve data based on partial matches rather than exact matches. The two most commonly used wildcards in SQL are the percent sign (%) and the underscore (_). The percent sign represents zero or more characters, while the underscore represents a single character.
For instance, if a developer wants to find all customer names that start with "J" in a database, they can use the query: SELECT * FROM Customers WHERE CustomerName LIKE 'J%'. This will return all records where the CustomerName begins with "J", regardless of what follows. Similarly, if someone wants to find names that contain the letter "a" in the second position, the query would look like: SELECT * FROM Customers WHERE CustomerName LIKE '_a%'. Here, the underscore signifies that there should be one character before the letter "a", allowing developers to target specific patterns in their data.
Wildcards can be combined with other SQL clauses to refine search results further. For example, you can use them with the WHERE clause to filter records based on certain conditions besides string matching. Developers can also use wildcards in more complex situations, such as searching within joined tables or applying them in subqueries. This flexibility makes wildcards an essential tool in SQL for conducting detailed searches and managing data effectively.