在create table的語句中,key和index混淆在一起,官方手冊中的解釋是這樣:
KEY
is normally a synonym forINDEX
. The key attributePRIMARY KEY
can also be specified as justKEY
when given in a column definition. This was implemented for compatibility with other database systems.KEY通常是INDEX的同義詞。當在列定義中給出時,鍵屬性PRIMARY KEY也可以被指定為KEY。這是為了與其他數據庫系統兼容而實現的。