Create table students
(
  Sid  number(3),
  Sname varchar(20)  not null,
  Email varchar(20)  not null,
  Doj  Timestamp    default    sysdate    not null,
  Dob  date     not null,
  Phno number(10),
  Address varchar(20),
  Resume LONG,
  Gender char(1) Default  'M',
  Cid  number,
  Constraint Pk_stu_sid  Primary key(sid,cid),
  Constraint Un_stud_email Unique(email),
  Constraint  chk_stud_email Check(email like '%@%.%'),
  Constraint chk_stud_phno Check(length(phno) = 10),
  Constriant chk_stud_gender Check(gender in ('M','F')),
  Constraint Fk_stud_cid foreign key(cid) references
          course(cid))
)

SQL> 
SQL> Create table students
  2  (
  3    Sid  number(3),
  4    Sname varchar(20)  not null,
  5    Email varchar(20)  not null,
  6    Doj  Timestamp    default    sysdate    not null,
  7    Dob  date     not null,
  8    Phno number(10),
  9    Address varchar(20),
 10    Resume LONG,
 11    Gender char(1) Default  'M',
 12    Cid  number,
 13    Constraint Pk_stu_sid  Primary key(sid,cid),
 14    Constraint Un_stud_email Unique(email),
 15    Constraint  chk_stud_email Check(email like '%@%.%'),
 16    Constraint chk_stud_phno Check(length(phno) = 10),
 17    Constriant chk_stud_gender Check(gender in ('M','F')),
 18    Constraint Fk_stud_cid foreign key(cid) references
 19            course(cid))
 20  )
 21  /
  Constriant chk_stud_gender Check(gender in ('M','F')),
                                                       *
ERROR at line 17:
ORA-02438: Column check constraint cannot reference other columns