Sql unique varchar case sensitivity question

The quirks of SQL case-sensitivity

Generally, SQL's UNIQUE constraint operates in a case-insensitive manner, ignoring the differences between uppercase and lowercase characters. However, there are ways to tweak your SQL to consider these differences and maintain case-sensitive uniqueness.

Applying the utf8_bin collation to your column

To use VARCHAR field for case-sensitive uniqueness, you can apply the utf8_bin collation directly:

ALTER TABLE Users 
MODIFY Username VARCHAR(50) 
CHARACTER SET utf8 
COLLATE utf8_bin UNIQUE;


This application now ensures 'Seth' and 'seth' are considered as distinct values. Now, that's equal opportunity!

Switching to VARBINARY

Another route you could take is switching to VARBINARY in place of VARCHAR. This shift not only maintains case sensitivity, but it also considers trailing spaces:

ALTER TABLE Users 
MODIFY Username VARBINARY(50) UNIQUE;


This change means no hat left behind (spaces included). However, remember this also means alteration to sorting and comparison operations.

Understanding binary collation

The Benefits

• Exact matches: Binary collation allows your queries to match entries precisely, enhancing data integrity.
• Language sensitivity: For languages where case holds meaning, this is essential.

The Drawbacks

• User experience: Users would need to remember exact capitalization. Sounds like a password recovery nightmare!
• Locale-specific issues: Binary collation sidesteps locale-specific case rules. So, multinational users, beware!

Cases and sensitivity: time to test!

Before going live, ensure you're thoroughly validating your application by creating scenarios with entries that contrast only in case. Monitor how your database enforces this constraint.

Making the most of your SQL system

Whether you're using MySQL, PostgreSQL, SQL Server, or SQLite, they all have systems that can accommodate case sensitivity with variations:

• PostgreSQL supports a range of collations, which can be adapted for case sensitivity.
• SQL Server makes use of Latin1_General_BIN2 as a collation for a UNIQUE constraint to achieve the same goal.
• For SQLite, leaving out COLLATE NOCASE implies case-sensitive behavior by default.

As each SQL system could have its nuance, your investment in reading the documentation would pay off.