List of special characters for SQL LIKE clause

Extended character matching and negation

A feature in some SQL flavors, [] and [^] notations allow matching any single character within, or outside, a specified set respectively. However, not universally supported.

Search within character range:

-- "In a range from a to c, but no 'd" for danger'"
SELECT * FROM table_name WHERE column_name LIKE '[a-c]%';
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Search outside character range:

-- "'a' for apple, 'b' for banana? Not today."
SELECT * FROM table_name WHERE column_name LIKE '[^a-c]%';
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The outcomes of using character sets could be affected by the database collation, changing how ranges are recognized.

Dialects of SQL: special symbols

Special characters can vary across SQL dialects. For instance, PostgreSQL provides SIMILAR TO operator which enables regular expression patterns:

PostgreSQL's SIMILAR TO

-- "Catch 'abc' or 'def', but don't 'ghi've up on others!"
SELECT * FROM table_name WHERE column_name SIMILAR TO '%(abc|def)%';
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This code uses special characters | for alternatives, * for repetitions, and + and () for grouping.

Real-world use cases and potential pitfalls

The implementation of special characters boosts search capabilities but complicates DBMS portability. Be wary of:

• Escaping literals: Different databases escape LIKE wildcards differently ('\' , '!' , '[]'). Check the documentation accordingly.
• Case sensitivity: For instance, SQL Server is case insensitive by default, PostgreSQL isn't. A pattern like 'A%' may yield different results.
• Database collation: Impacts how ranges ([a-c]%) are interpreted in the LIKE clause.

Rooms for caution

Ensure caution to prevent wildcard injection where unsanitised user input could introduce expensive wildcard searches.

Also, leading wildcards (LIKE '%term') can be performance-intensive, as they may need to perform full table scans.

Trust the Book (documentation)

This answer provides a rock-solid foundation, however, the official documentation for your database system will be the definitive guide. They might contain unique nuances or additional special characters.

Spreading Knowledge

Forge a community wiki for SQL LIKE clause special characters. This would be a living document on idiosyncrasies across different databases and a testament of your collaborative spirit.