1.MySQL的schema和database的区别
    https://dev.mysql.com/doc/refman/8.0/en/glossary.html#glos_schema
    https://dev.mysql.com/doc/refman/8.0/en/glossary.html#glos_database
    https://stackoverflow.com/questions/7942520/relationship-between-catalog-schema-user-and-database-instance

    2.MySQL中modify和change的区别
    modify可以修改字段的类型和顺序。 change可以修改字段的名字和类型。
    modify只需要写一次名称，change需要写旧名称和新名称。

    3.value和values的区别
    VALUE is a synonym for VALUES in this context. Neither implies anything about the number of values lists, nor about the number of values per list. Either may be used whether there is a single values list or multiple lists, and regardless of the number of values per list.
    https://dev.mysql.com/doc/refman/8.0/en/insert.html