constraint

1、添加主键约束

SQL> desc kaoqin;
 Name                                      Null?    Type
 ----------------------------------------- -------- ----------------------------
 ID                                                 NUMBER(38)
 NAME                                               VARCHAR2(10)
 UPTIME                                             DATE
 DOWNTIME                                           DATE

SQL> select * from kaoqin ;

no rows selected

SQL> alter table kaoqin add primary key (id);

Table altered.