SQL的分類
DDL(data definition languages)
數據定義語言
create
alter
alter table tablename [add |modify | drop ] column column_name column_type column_define;
mysql> create table dept(deptno int not null auto_increment, deptname varchar(10));
ERROR 1075 (42000): Incorrect table definition; there can be only one auto column and it must be defined as a key
mysql> create table dept(deptno int not null auto_increment primary key, deptname varchar(10));
Query OK, 0 rows affected (0.03 sec)
一張表只有一個主鍵
auto_increment(自動增長) 一定要有primary key,
primary key 不一定有auto_increment.
DML(data manipulation language)
數據操縱語言
DCL(data control language)
數據 控制語句