Finding the Hidden Meaning: How to Escape Underscores in SQL Server Queries

• In SQL Server's LIKE operator, used for pattern matching in queries, certain characters have special meanings:
  • %: Matches zero or more of any character.
  • _: Matches any single character.

When to Escape Underscores

• If you want to search for an actual underscore (_) within your data, you need to escape it. This is because the underscore is a wildcard by default.

Escaping Methods

1. Backslash ():

   • Precede the underscore with a backslash (\) to treat it literally.
   • Example: SELECT * FROM MyTable WHERE Name LIKE '%\_smith%' ESCAPE '\'

2. Character Brackets ([]):

   • Enclose the underscore within square brackets ([]) to treat it as a single character.

Choosing the Right Method

• Both methods achieve the same result.
• Backslash escaping is often preferred due to its wider compatibility across different database systems.
• Character bracket escaping might be more readable for simpler patterns.

Example:

Suppose you have a table named People with a Name column containing values like "John_Doe", "Jane_Smith", and "Alex Jones".

• To find names containing an underscore, use:

  SELECT * FROM People WHERE Name LIKE '%\_%';
  

  This will return "John_Doe" and "Jane_Smith".

Additional Considerations

• The escape character you choose (\ in this case) can be any valid character that won't conflict with your pattern.
• Be mindful of escaping other special characters if they appear in your search pattern.

-- Find names containing an underscore
SELECT * FROM People WHERE Name LIKE '%\_% ESCAPE '\' ESCAPE '\';

-- Find names starting with "Alex_" (underscore included)
SELECT * FROM People WHERE Name LIKE '\_Alex%' ESCAPE '\';

Character Bracket Escape:

-- Find names containing an underscore
SELECT * FROM People WHERE Name LIKE '%[_%]';

-- Find names starting with "Alex_" (underscore included)
SELECT * FROM People WHERE Name LIKE '[_]Alex%';

Explanation:

• The ESCAPE '\' clause specifies the backslash (\) as the escape character in both methods.
• In the first example of each method, %\_% searches for any string containing an underscore (_).
• In the second example, \_Alex% (with backslash escape) or [_]Alex% (with character bracket escape) searches for names starting with "Alex_" (including the underscore).

1. Regular Expressions (SQL Server 2017 and Later):

2. Avoiding LIKE Operator Altogether: