Defining integrity constraint using Alter table

Create table sales(icode number(5),na varchar2(20),qty number(5));
            Create table sales1(icode number(5),na varchar2(20),qty number(5));

• alter table sales add primary key(icode);
• alter table sales1 add constraint f_key foreign key(icode) REFERENCES sales
• alter table sales1 modify (qty number(5) NOT NULL);
• alter table sales drop primary key;
• alter table sales drop constraint f_key;

  Disable
              It is used to disable all integrity constants of the tables
  Syn:- disable [unique][primary key][check][alltriggers]
  Ex:-   alter table sales disable primary key ;
  alter table sales disable constraint f_key;
  Enable
              It is used to enable all the disable triggers.
  Ex:-   alter table sales enable primary key ;
  alter table sales enable constraint f_key;

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