In SQL, wildcards are special characters used in queries to represent one or more characters, allowing for pattern matching during searches. The two most common wildcards are the percentage symbol (%) and the underscore (_). The percentage symbol represents zero or more characters, while the underscore represents a single character. These wildcards can be particularly useful in LIKE clauses, where you want to search for data that fits a certain pattern without needing to provide the exact string.
For example, if you want to find all customer names in a database that start with the letter "J," you can use the following query: SELECT * FROM Customers WHERE Name LIKE 'J%';. This query retrieves all records where the Name starts with "J" and may have any characters following it. Similarly, if you want to find names that have "an" anywhere in them, you can use: SELECT * FROM Customers WHERE Name LIKE '%an%';. This returns any name that contains the substring "an," regardless of what comes before or after.
Additionally, the underscore wildcard can be useful when you want to match a specific number of characters. For example, if you are looking for names that have five letters and the second letter is "a," the query would be: SELECT * FROM Customers WHERE Name LIKE '_a___';. Here, the underscore placeholders represent each character you want to account for. Overall, wildcards greatly enhance your ability to perform flexible searches in SQL, making it easier to retrieve information from databases based on partial matches.