SQL Wildcards – How to Search Smarter with Flexible Patterns

When working with SQL, there are times you need to search for patterns in your data instead of exact matches. That’s where wildcards come in. I had a hard time with them when I was learning, now I am here to help you!

Wildcards are special characters used with the LIKE operator to find values that fit a certain pattern. They’re especially useful when you’re dealing with incomplete data, unknown characters, or flexible search criteria.

In this post, you’ll learn the most common SQL wildcards, what they mean, and how to use them effectively with examples.

Table of Contents

1. What Are SQL Wildcards?
2. Using the LIKE Operator
3. Common SQL Wildcards and Their Meanings
4. Wildcard Examples in Action
5. Tips for Using Wildcards Effectively
6. Wildcards in Different SQL Dialects
7. Common Mistakes to Avoid
8. Conclusion

What Are SQL Wildcards?

SQL wildcards are special characters that help you search for patterns in text data instead of exact matches. They are most commonly used with the LIKE operator in SQL queries. Imagine you’re looking for all names that start with the letter “A”, instead of listing each one, you can use a wildcard to make your query more flexible and powerful. Wildcards make it easier to find results even when you don’t know the full value you’re searching for. They’re super useful when dealing with incomplete information, user-generated content, or when you just want to filter text in a more dynamic way. Think of them as shortcuts that help your SQL queries “guess” what you’re trying to find.

Using the LIKE Operator

The LIKE operator in SQL is used to search for a specific pattern in a column, usually combined with wildcards to make the search more flexible. Instead of looking for an exact match, LIKE helps you filter results based on what the value contains, starts with, ends with, or how it’s structured.

For example, if you write WHERE name LIKE ‘A%’, it will return all names that start with the letter A, such as “Alice” or “Andrew.” You can also use it to find names that contain a certain pattern, like ‘%son%’ to match “Jackson” or “Emerson.” It’s especially powerful when you don’t have the full data or want to match multiple similar values.

Is LIKE case sensitive?

The LIKE operator is case-insensitive in some databases like SQL Server but case-sensitive in others like PostgreSQL, unless you use specific functions. That’s something to keep in mind depending on the SQL version you’re working with.

You can use LIKE with wildcards such as % for any number of characters or _ for just one character. This allows for very detailed pattern matching, like finding values that are exactly four characters long (‘__‘) or have a specific character in the middle (‘a‘). Just remember, LIKE is used with text-based columns like VARCHAR or CHAR, and it’s best not to overuse it in large datasets without indexing, because it can slow down performance. Still, it’s an essential tool for flexible filtering and can really level up your SQL queries.

Common SQL Wildcards and Their Meanings

SQL wildcards are symbols that represent one or more characters in a string and are mostly used with the LIKE operator to search for flexible patterns.

The most common wildcard is the percent sign %, which matches any number of characters, even zero. For example, ‘A%’ matches “A”, “Alex”, or “Apple.”

Another useful wildcard is the underscore _, which matches exactly one character, so ‘B_n’ would match “Ben” or “Bin,” but not “Brian.”

In SQL Server, you can use square brackets [ ] to match a single character from a specific set, like ‘t[ae]st’, which matches “test” or “tast.”

You can also reverse this logic using [^ ] or ![ ] to match any character not in the set, so ‘t[^ae]st’ matches “t1st” or “t9st,” but not “test” or “tast.”

Inside the brackets, you can also use the dash – to define a range of characters, such as ‘[a-z]’ for all lowercase letters.

These wildcards make SQL powerful for pattern searching, especially when data isn’t consistent or when you’re looking for trends or categories within a column.

Wildcard Examples in Action

Let’s look at some examples to see how SQL wildcards work in real-life queries.

Suppose you have a table called customers and you want to find all names that start with the letter “J”—you can write

SELECT *
FROM customers 
WHERE name LIKE 'J%'

Using wildcards in SQL can be very powerful, but to use them effectively, there are a few tips to keep in mind:

1. First, always be as specific as possible with your patterns, starting a search with % (like ‘%name’) can be slow on large datasets because the database has to scan every record.
2. Instead, try to anchor your pattern when you can, like ‘name%’, which is usually faster.
3. Use underscores _ when you know the exact number of characters to match, which is great for things like ID formats or codes.
4. If you’re working in SQL Server and using bracket wildcards, remember that the pattern is case-sensitive unless configured otherwise, so you may need to handle both uppercase and lowercase manually.
5. Also, avoid overusing wildcards in complex queries where performance matters, it’s better to combine them with indexed columns or other filters when possible.
6. And finally, always test your pattern with a few different cases to make sure it’s matching what you expect. A small typo or misunderstanding in how the wildcard works can lead to either missing data or returning too much.

Wildcards in Different SQL Dialects

Wildcards work similarly in most SQL dialects, but there are some important differences you should know depending on which database system you’re using.

The basic wildcards % (for any number of characters) and _ (for a single character) are supported in almost all SQL dialects, including MySQL, PostgreSQL, SQLite, and SQL Server. However, things change a bit when it comes to more advanced wildcard features. For example, SQL Server supports square brackets [ ] for specifying character ranges or sets, like ‘[a-c]’ or ‘[xyz]’, and it also supports [^ ] or ![ ] for negation inside brackets. These bracket patterns are not supported in MySQL or PostgreSQL.

In PostgreSQL, if you need more advanced pattern matching, you might use the SIMILAR TO or even regular expressions with ~ or ~* operators.

MySQL also supports REGEXP for more flexible pattern searching beyond LIKE.

So while the basic use of % and _ is consistent, it’s important to check the specific features and functions your SQL dialect supports if you want to go beyond the basics. Knowing these differences helps avoid confusion and lets you write more effective queries, especially when switching between systems.

Common Mistakes to Avoid

When working with SQL wildcards, there are some common mistakes that beginners (and even experienced users) often make.

One big mistake is putting wildcards in the wrong place, for example, using ‘%’ in the middle or end when you actually need it at the start to find values that end with something.

Another issue is forgetting that % matches zero characters, which means a pattern like ‘A%’ will also match just ‘A’, not only longer values.

Many people also confuse the % and _ symbols; remember that % is for any number of characters, while _ is exactly one.

In SQL Server, a common mistake is using brackets [ ] in other databases like MySQL or PostgreSQL, where they don’t work as wildcards at all.

Some users also assume wildcards are always case-insensitive, but this depends on the SQL dialect and collation settings, PostgreSQL, for example, treats LIKE as case-sensitive unless you use ILIKE.

Lastly, overusing wildcards, especially at the beginning of a pattern, can seriously hurt performance, especially on large datasets, so it’s a good habit to use them only when necessary and combine them with other filters when possible.

Conclusion

To wrap it all up, SQL wildcards are a simple but powerful tool that can make your searches much more flexible and efficient. Whether you’re trying to find names that start with a certain letter, match a specific pattern, or filter out unwanted results, wildcards give you that extra control. Once you understand how %, _, and other special characters like brackets work, especially across different SQL dialects, you’ll feel a lot more confident writing smarter queries. Just be careful with performance and test your patterns to make sure they return the results you expect. Keep practicing with small queries, and soon, using wildcards will feel like second nature. You’ve got this!