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

Question

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?

Answer 1

change database collation:

ALTER DATABASE <database_name> CHARACTER SET utf8 COLLATE utf8mb4_0900_ai_ci;

change table collation:

ALTER TABLE <table_name> CONVERT TO CHARACTER SET utf8 COLLATE utf8mb4_0900_ai_ci;

change column collation:

ALTER TABLE <table_name> MODIFY <column_name> VARCHAR(255) CHARACTER SET utf8 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 multiple letters; eg ss=ß, somewhat fast
...          -- slower
_0900_       -- (8.0) much faster because of a rewrite

More info:

• What are the differences between utf8_general_ci and utf8_unicode_ci?
• What's the difference between utf8_general_ci and utf8_unicode_ci?
• How to change collation of database, table, column?
• What's the difference between utf8_general_ci and utf8_unicode_ci?