columns to make sure they both exist and have the intended type
scripts/mysql_fix_privilege_tables.sql:
Can't attempt to MODIFY columns of a table before they exists. The
new column's Create_view_priv,Show_view_priv, Create_routine_priv,
Alter_routine_priv and Create_user_priv might not exists when
upgrading. Thus an ALTER TABLE MODIFY is added in addition to the
ALTER TABLE ADD that would have added them if they didn't exist.
In this way can be sure the columns both exist and are of the correct type
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