utf8_general_ci vs. utf8_unicode_ci: Which MySQL Unicode Collation Should I Choose?

utf8_general_ci vs. utf8_unicode_ci Collation Algorithms

MySQL offers two unicode collations, utf8_general_ci and utf8_unicode_ci, seemingly indistinguishable at first glance. However, their underlying collation algorithms differ significantly.

utf8_general_ci: Incorrect Unicode Handling

utf8_general_ci follows a simplified process: Unicode normalization, removal of combining characters, and uppercase conversion. This approach fails in Unicode environments due to its limited understanding of Unicode casing. For instance:

• Uppercase "ß" (U 00DF) yields "SS" instead of "ẞ".
• Greek has multiple lowercase sigmas, but only one uppercase variant.

utf8_unicode_ci: Standard Unicode Collation Algorithm

In contrast, utf8_unicode_ci employs the Unicode Collation Algorithm, providing accurate results for all scripts. It handles:

• Expansions and ligatures: ß is sorted near "ss," and Œ (U 0152) near "OE".
• Cyrillic: utf8_unicode_ci correctly sorts Cyrillic letters, which utf8_general_ci mishandles.

Impact on Database Design

Choosing the appropriate collation is crucial for data integrity. utf8_general_ci's incorrect handling of Unicode can lead to inconsistent sorting and retrieval. utf8_unicode_ci, although slightly slower, guarantees correct results, making it the preferred choice in internationalized databases.

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