Explain SQL Wildcard Characters

Introduction

When it comes to SQL (Structured Query Language), retrieving data efficiently is crucial. Wildcard characters are among the most effective methods for pattern matching in SQL. Finding the exact data you need is made easier with the use of wildcards, which allow you to define versatile query conditions. You will learn about the fundamentals and more complex uses of SQL wildcard characters in this article.

1. Percent (%)

Represents one, zero, or more characters.

Example

SELECT * FROM Employees WHERE LastName LIKE 'S%'

Finds any last names that start with the letter 'S'.

2. Underscore (_)

(_) is a single character's representation.

Example

SELECT * FROM Employees WHERE LastName LIKE '_a%'

Matches last names with the second letter being '

3. Square Brackets ([])

Used to define a range or set of characters.

Example

SELECT * FROM Employees WHERE LastName LIKE '[S-T]%'

Finds last names beginning with any letter from "S" to "T."

4. Caret (^) inside Square Brackets

Used to exclude a range or set of characters.

Example

SELECT * FROM Employees WHERE LastName LIKE '[^S]%'

Identifies last names that don't begin with the letter "S."

5. Hyphen (-) inside Square Brackets

Used to define a character range.

Example

SELECT * FROM Employees WHERE LastName LIKE '[A-D]%'

Finds last names beginning with any letter between "A" and "D."

Practical Examples

1. Finding Names Containing "Is"

SELECT * FROM Employees WHERE FirstName LIKE '%Is%'

2. Finding Names with Exactly Five Characters

SELECT * FROM Employees WHERE FirstName LIKE '_____'

3. Finding Names Starting with 'I', Followed by Any Two Characters, and Then 'S'

SELECT * FROM Employees WHERE FirstName LIKE 'I__S%'

4. Finding Names Starting with 'A' or 'B'

SELECT * FROM Employees WHERE FirstName LIKE '[AB]%'

5. Finding Names Not Starting with 'M' or 'N'

SELECT * FROM Employees WHERE FirstName LIKE '[^MN]%'

6. Names Starting with 'A', Containing 'n', and Ending with 'y'

SELECT * FROM Employees WHERE FirstName LIKE 'A%n%y'

7. Names with the Second Letter as 'a' and the Fourth Letter as 'e'

SELECT * FROM Employees WHERE FirstName LIKE '_a_e%'

Conclusion

Gaining proficiency with SQL wildcard characters improves your ability to get data by enabling accurate and versatile pattern matching. When combined with the LIKE operator, these characters facilitate effective pattern recognition. Even with big datasets, query efficiency can be increased by being aware of their use and performance consequences. Using wildcards will help you narrow down your searches and analyze data more efficiently, which will improve your overall SQL skills.


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