What's the difference between utf8_general_ci and utf8_unicode_ci?

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utf8_general_ci and utf8_unicode_ci are two different collation (sorting and comparison) methods for text in MySQL databases when dealing with character sets like UTF-8. They have differences in how they compare and sort text, particularly in cases involving accents and special characters.

  1. utf8_general_ci (General Collation):

    • Case-insensitive: It treats uppercase and lowercase letters as equivalent during comparisons. For example, 'A' and 'a' are considered the same.
    • Accent-insensitive: It treats accented characters as equivalent to their unaccented counterparts. For example, 'é' and 'e' are considered the same.
    • Faster: Generally, it performs slightly faster than utf8_unicode_ci because of its simpler comparison rules.

  2. utf8_unicode_ci (Unicode Collation):

    • Case-insensitive: Like utf8_general_ci, it treats uppercase and lowercase letters as equivalent during comparisons.
    • Accent-sensitive: It distinguishes between accented characters and their unaccented counterparts. For example, 'é' and 'e' are not considered the same.
    • Supports a wider range of languages: It provides better support for a wide variety of languages, particularly those with complex collation rules, thanks to its adherence to the Unicode standard.

Here's a simple example to illustrate the difference between these collations:

sql
-- Create a table with utf8_general_ci collation
CREATE TABLE general_collation (
    name VARCHAR(255) COLLATE utf8_general_ci
);

-- Insert data
INSERT INTO general_collation (name) VALUES ('apple'), ('banana'), ('Éclair'), ('elk');

-- Query with a case-insensitive search
SELECT * FROM general_collation WHERE name = 'éclair';
-- Result: Éclair

-- Create a table with utf8_unicode_ci collation
CREATE TABLE unicode_collation (
    name VARCHAR(255) COLLATE utf8_unicode_ci
);

-- Insert data
INSERT INTO unicode_collation (name) VALUES ('apple'), ('banana'), ('Éclair'), ('elk');

-- Query with a case-insensitive search
SELECT * FROM unicode_collation WHERE name = 'éclair';
-- Result: Éclair, elk

In the utf8_general_ci table, the search for 'éclair' returns a match for 'Éclair' because it's case-insensitive and accent-insensitive. In the utf8_unicode_ci table, the search returns both 'Éclair' and 'elk' because it's case-insensitive but accent-sensitive.

The choice between utf8_general_ci and utf8_unicode_ci depends on your specific requirements. If you need better support for a wide range of languages and want to distinguish between accented and unaccented characters, utf8_unicode_ci is usually a better choice. If you need slightly better performance and don't require fine-grained language support, utf8_general_ci may suffice.

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