_ (Wildcard - Match One Character) (Transact-SQL)

Applies to: SQL Server Azure SQL Database Azure SQL Managed Instance

Use the underscore character _ to match any single character in a string comparison operation that involves pattern matching, such as LIKE and PATINDEX.

Examples

A: Simple example

The following example returns all database names that begin with the letter m and have the letter d as the third letter. The underscore character specifies that the second character of the name can be any letter. The model and msdb databases meet this criteria. The master database does not.

SELECT name FROM sys.databases
WHERE name LIKE 'm_d%';

Here's the result set.

name
-----
model
msdb

You may have additional databases that meet this criteria.

You can use multiple underscores to represent multiple characters. Changing the LIKE criteria to include two underscores 'm__% includes the master database in the result.

B: More complex example

The following example uses the _ operator to find all the people in the Person table, who have a three-letter first name that ends in an.

-- USE AdventureWorks2022;
  
SELECT FirstName, LastName  
FROM Person.Person  
WHERE FirstName LIKE '_an'  
ORDER BY FirstName;  

C: Escaping the underscore character

The following example returns the names of the fixed database roles like db_owner and db_ddladmin, but it also returns the dbo user.

SELECT name FROM sys.database_principals
WHERE name LIKE 'db_%';

The underscore in the third character position is taken as a wildcard, and is not filtering for only principals starting with the letters db_. To escape the underscore enclose it in brackets [_].

SELECT name FROM sys.database_principals
WHERE name LIKE 'db[_]%';

Now the dbo user is excluded.

Here's the result set.

name
-------------
db_owner
db_accessadmin
db_securityadmin
...

See Also

LIKE (Transact-SQL)
PATINDEX (Transact-SQL)
% (Wildcard - Character(s) to Match)
[ ] (Wildcard - Character(s) to Match)
[^] (Wildcard - Character(s) Not to Match)