How to Use Java Regular Expressions to Mimic SQL LIKE Clause Syntax

What is the Java RegEx equivalent for the SQL LIKE clause syntax %A%B%?

String regex = ".*A.*B.*";

In SQL, the LIKE clause is used to search for a specified pattern in a column. The '%' wildcard represents zero or more characters. In Java, the equivalent functionality can be achieved using Regular Expressions (RegEx). To mimic the SQL pattern '%A%B%', we will translate the wildcard use into regular expression syntax.

import java.util.regex.Pattern;
import java.util.regex.Matcher;

String input = "ABCD";
String regex = ".*A.*B.*";
Pattern pattern = Pattern.compile(regex);
Matcher matcher = pattern.matcher(input);
boolean matches = matcher.matches(); // returns true if the input matches the regex.

Causes

• Understanding the basics of SQL LIKE clause and its wildcards.
• Recognizing how to translate SQL syntax to Java RegEx terms.

Solutions

• In Java, use '.*' to represent any character sequence (equivalent to SQL '%'). For example, to check for patterns like '%A%B%', the RegEx pattern would be '.*A.*B.*'.
• Utilize the Pattern and Matcher classes in Java to implement and test the regex against strings.

Mistake: Misunderstanding the '.' in regex, which matches any single character, not a wildcard for zero or more characters.

Solution: Use '.*' to represent any sequence of characters instead.

Mistake: Not escaping special characters in regular expressions, such as '.' or '*'.

Solution: Always ensure special characters are escaped using double backslashes in Java.