Create table user ( id number (3),  USERNAME VARCHAR2 (    PASSWORD VARCHAR2), Cid number (3), sex varcher (4)); Create table card ( id number (3), name VARCHAR2 (10)); --Add primary key Alter table user add constraint uaer_pk primary key (ID); --Add foreign Key Alter table user add constraint uaer_fk foreign key (CID) References card (ID); --Add Check constraint alter table user add constraint uaer_chk check (sex in ) (' Boy ', ' Girl ')); ---------------\ \ Operation Column alter table tablename add (columnname datatype[default value ][null/not null],......); --Add Column alter table tablename modify (columnname datatype[default vAlue][null/not null],......); --Modify Column Alter table tablename drop (ColumnName);--Delete Column Alter table tablename rename column col_old_name to col_new_name;--Modify Column Name--add column alter table user add (AA varchar2 default ' aaaa ' not null); --Modifying column alter table user modify (USERNAME VARCHAR2 (1000)); --Delete column alter table user drop (password); --Modify Column name alter table user rename column username to username_new; ----------------\ \ Compile the specified object: process: alter procedure procedure_name compile; function: alter function funtion_name compile; Package: alter package package_name compile; Package Body: alter package package_name compile body; ----------------\ \ Move the index to the T_IDX Index table space alter index user_pk rebuild tablespace t_idx; \ \ Create path create or replace directory dir_cust as '/oracle/aaa '; \ \ Move the table to the tb_t table space alter table user move tablespace tb_t---------------------------------- -------------------------\ \ Main foreign key effective failure Alter table user disable constraint uaer_pk ; Alter table user enable constraint uaer_pk ; \ \ Trigger Invalid alter table user disable all triggers; alter table user enable all triggers; \ Unlock alter user zzz account unlock;