12.3.2 Server Character Set and Collation

MySQL Server has a server character set and a server collation. By default, these are utf8mb4 and utf8mb4_0900_ai_ci, but they can be set explicitly at server startup on the command line or in an option file and changed at runtime.

Initially, the server character set and collation depend on the options that you use when you start mysqld. You can use --character-set-server for the character set. Along with it, you can add --collation-server for the collation. If you don't specify a character set, that is the same as saying --character-set-server=utf8mb4. If you specify only a character set (for example, utf8mb4) but not a collation, that is the same as saying --character-set-server=utf8mb4 --collation-server=utf8mb4_0900_ai_ci because utf8mb4_0900_ai_ci is the default collation for utf8mb4. Therefore, the following three commands all have the same effect:

mysqld
mysqld --character-set-server=utf8mb4
mysqld --character-set-server=utf8mb4 \
  --collation-server=utf8mb4_0900_ai_ci

Character set and collation startup options require explicit names. --character-set-server accepts exactly one value; multiple values are rejected. The value utf8 is rejected for this option, and utf8_* collation names are rejected for --collation-server. Use explicit utf8mb3, utf8mb4, utf8mb3_*, or utf8mb4_* names. These restrictions also apply to settings read from option files.

One way to change the settings is by recompiling. To change the default server character set and collation when building from sources, use the DEFAULT_CHARSET and DEFAULT_COLLATION options for CMake. For example:

cmake . -DDEFAULT_CHARSET=latin1

Or:

cmake . -DDEFAULT_CHARSET=latin1 \
  -DDEFAULT_COLLATION=latin1_german1_ci

Both mysqld and CMake verify that the character set/collation combination is valid. If not, each program displays an error message and terminates.

The server character set and collation are used as default values if the database character set and collation are not specified in CREATE DATABASE statements. They have no other purpose.

The current server character set and collation can be determined from the values of the character_set_server and collation_server system variables. These variables can be changed at runtime.