mysqlsqlcollation

How to change the CHARACTER SET (and COLLATION) throughout a database?

Our previous programmer set the wrong collation in a table (Mysql). He set it up with Latin collation, when it should be UTF8, and now I have issues. Every record with Chinese and Japan character turn to ??? character.

Is possible to change collation and get back the detail of character?

Solution

  • change database collation:

    ALTER DATABASE <database_name> CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

    change table collation:

    ALTER TABLE <table_name> CONVERT TO CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

    change column collation:

    ALTER TABLE <table_name> MODIFY <column_name> VARCHAR(255) CHARACTER SET utf8mb4 COLLATE utf8mb4_0900_ai_ci;

    What do the parts of utf8mb4_0900_ai_ci mean?

    3 bytes -- utf8
4 bytes -- utf8mb4 (new)

    v4.0 --   _unicode_
v5.20 --  _unicode_520_
v9.0 --   _0900_ (new)

    _bin      -- just compare the bits; don't consider case folding, accents, etc
_ci       -- explicitly case insensitive (A=a) and implicitly accent insensitive (a=á)
_ai_ci    -- explicitly case insensitive and accent insensitive
_as (etc) -- accent-sensitive (etc)

    _bin         -- simple, fast
_general_ci  -- fails to compare multiletters; eg ss=ß, somewhat fast
...          -- slower
_0900_       -- (8.0) much faster because of a rewrite

    More info: