Mysql：Changes in MySQL 5.7.13 (2016-06-02, General Availability)：maximum length of MySQL user names was increased from 16 to 32 characters

Changes in MySQL 5.7.13 (2016-06-02, General Availability)

Account Management Notes

In MySQL 5.7.8, the maximum length of MySQL user names was increased from 16 to 32 characters, but some applicable contexts for this increase were overlooked. Additional changes in maximum user name length now have been applied:
- The size of these mysql system table columns is increased:
  - The definer column of the event and proc tables
  - The grantor column of the procs_priv and tables_priv tables
  In each case, the column previously was defined as CHAR(77), where 77 was chosen to permit a user_name@host_name string containing a user name up to 16 characters, a @ character, and a host name up to 60 characters. Each column now is defined as CHAR(93), reflecting an increase in permitted user name length from 16 to 32 characters.
- A similar change from CHAR(77) to CHAR(93)applies to the DEFINER column of these INFORMATION_SCHEMA tables: EVENTS, ROUTINES, TRIGGERS, VIEWS. Along with the changes to INFORMATION_SCHEMA tables, output from any corresponding SHOW statements now displays DEFINER values up to 93 characters. Examples of affected statements: SHOW EVENTS, SHOW TRIGGERS, SHOW PROCEDURE STATUS.
If you upgrade to this MySQL release from an earlier version, you must run mysql_upgrade (and restart the server) to incorporate the changes to the mysql system database. A server from MySQL 5.7.13 or higher for which mysql_upgrade has not been run continues to permit a maximum of 77 characters in the system tables mentioned previously, and an ER_USER_COLUMN_OLD_LENGTH error will occur in those system table contexts where a user_name@host_name value from 78 to 93 characters long is given.

It is possible to use ALTER TABLE to change the default value of a column col_name, which may change the value of a generated column expression that refers to the column using DEFAULT(col_name). For this reason, ALTER TABLE operations that change the definition of a column now cause a table rebuild if any generated column expression uses DEFAULT(). (Bug #80299, Bug #22680839)

It is possible to use ALTER TABLE to change the default value of a column col_name, which may change the value of a generated column expression that refers to the column using DEFAULT(col_name). For this reason, ALTER TABLE operations that change the definition of a column now cause a table rebuild if any generated column expression uses DEFAULT().

原文地址：https://www.cnblogs.com/jinzhenshui/p/12584082.html