What does collation mean?

Question

What does collation mean in SQL, and what does it do?

Answer 1

Rules that tell how to compare and sort strings: letters order; whether case matters, whether diacritics matter etc.

For instance, if you want all letters to be different (say, if you store filenames in UNIX), you use UTF8_BIN collation:

SELECT  'A' COLLATE UTF8_BIN = 'a' COLLATE UTF8_BIN

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If you want to ignore case and diacritics differences (say, for a search engine), you use UTF8_GENERAL_CI collation:

SELECT  'A' COLLATE UTF8_GENERAL_CI = 'ä' COLLATE UTF8_GENERAL_CI

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As you can see, this collation (comparison rule) considers capital A and lowecase ä the same letter, ignoring case and diacritic differences.