Mastering SQL Wildcards: A Comprehensive Guide

SQL wildcards are essential tools for database developers and administrators who work with data retrieval and manipulation. This guide will help you understand SQL wildcards, their various types, and how to use them effectively in your queries. We will also demonstrate their usage with practical examples, and provide a handy diagram for reference.

SQL wildcards are special characters used in SQL queries to match patterns in string values. They provide flexibility when searching for records with specific characteristics or patterns within a database. By leveraging wildcards, you can create more efficient and dynamic queries that return the desired data without the need for exact matches.

There are several types of SQL wildcards, each with its unique capabilities and use cases. Understanding these wildcards will enable you to harness their full potential in your SQL queries.

The percent sign (%) wildcard is used to represent any sequence of zero or more characters. It is often employed in the LIKE clause to filter results based on partial matches.

SELECT * FROM employees WHERE last_name LIKE 'Smi%';

The underscore (_) wildcard represents any single character. It is also used in conjunction with the LIKE clause for pattern matching.

SELECT * FROM employees WHERE last_name LIKE 'A_a%';

Square brackets ([]) allow you to define a specific set or range of characters in a pattern. They are used in the LIKE clause of SQL Server and MS Access databases.

SELECT * FROM employees WHERE last_name LIKE '[C-F]%';\

> The caret (^) wildcard, when used within square brackets, negates the character set. It is supported in SQL Server and MS Access databases within the LIKE clause.

SELECT * FROM employees 
WHERE last_name LIKE '[^C-F]%';

The dash (-) wildcard, when used inside square brackets, represents a range of characters. It is supported in SQL Server

Question: How are SQL Wildcard Characters used in PL/SQL?
In PL/SQL, wildcard characters are used in SQL statements to represent unknown or variable values. The three commonly used wildcard characters are the percent sign (%), underscore (_), and square brackets ([]). The percent sign (%) is used to represent zero or more characters in a string. For example, if you want to select all customers whose name starts with the letter "J", you can use the following SQL statement:

SELECT * FROM customers WHERE name LIKE 'J%';

The underscore (_) is used to represent a single character in a string. For example, if you want to select all customers whose name is four letters long and starts with the letter "J", you can use the following SQL statement:

SELECT * FROM customers WHERE name LIKE 'J___';

The square brackets ([]), also known as the range wildcard, are used to match any character in a specified range. For example, if you want to select all customers whose name starts with the letters "J", "K", or "L", you can use the following SQL statement:

SELECT * FROM customers WHERE name LIKE '[JKL]%';

In PL/SQL, you can use these wildcard characters in SQL statements that are embedded within your code. For example, if you want to select a set of rows from a table based on some user input, you can use the wildcard characters to construct a dynamic SQL statement that matches the input. You can then execute this SQL statement using the EXECUTE IMMEDIATE statement or the OPEN-FOR statement.