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 Drop Command (DDL) in SQL Oracle With Implementation For Explanation Watch Video:: Drop Command Used to delete  table (rows X columns) EX::: 1)Create table SQL> create table emp01(fname varchar2(15),sal Number(10)); Table created. 2)Describe table SQL> desc emp01;  Name                                      Null?    Type  ----------------------------------------- -------- ----------------------------  FNAME                                              VARCHAR2(15)  SAL                                                NUMBER(10) SQL> select * from emp01; no rows selected 3)Insert values into table SQL> insert into emp01 values('smith',500000); 1 row created. 4)Drop the table SQL> drop table emp01; Table dropped. 5)TO see columns deleted again describe table SQL> desc emp01; ERROR: ORA-04043: object emp01 does not exist 6_to see data deleted SQL> select * from emp01; select * from emp01               * ERROR at line 1: ORA-00942: table or view does not exist

 Truncate Command (DDL) in SQL Oracle With Implementation For Explanation Watch Video:: Truncate:    -TO delete all rows from table at a time    - Deleting rows but not column    - By using this cmd we cant delete specific row from table    -It doesnt support where clause EX::: SQL> create table emp01(fname varchar2(10),sal Number(10)); Table created. SQL> insert into empo1 values('miller',500000); insert into empo1 values('miller',500000)             * ERROR at line 1: ORA-00942: table or view does not exist SQL> insert into emp01 values('miller',500000); 1 row created. SQL> insert into emp01 values('Baburao',50000); 1 row created. SQL> insert into emp01 values('Smith',500000); 1 row created. SQL> select * from emp01; FNAME             SAL ---------- ---------- miller         500000 Baburao         50000 Smith          500000 SQL> truncate table emp01; Table truncated. After Truncate:: SQL> select * from emp01; no rows se

 Primary Key::constraint ======================  ->It is combination of Unique and not null ->Restricted Duplicates and Nulls ->A table is having Only one primary Key At column Level:: ================= EX:: SQL> create table test2(eid int primary key,ename varchar2(10) primary key); create table test2(eid int primary key,ename varchar2(10) primary key)                                                           * ERROR at line 1: ORA-02260: table can have only one primary key SQL> create table test2(eid int primary key,ename varchar2(10)); Table created. SQL> insert into test2 values(1,'sam'); 1 row created. SQL> insert into test2 values(2,'dan'); 1 row created. SQL> select * from test2;        EID ENAME ---------- ----------          1 sam          2 dan SQL> insert into test2 values(null,'dan'); insert into test2 values(null,'dan')                          * ERROR at line 1: ORA-01400: cannot insert NULL into ("SYSTEM&quo

  Check Constraint::   ->to check values before accepting into a column with user defined condition at column level:: ================ >create table test1(eid int check(eid<5),ename varchar2(10)); EX:: SQL> create table test1(eid int check(eid<5),ename varchar2(10)); Table created. SQL> insert into test1 values(1,'dan'); 1 row created. SQL> insert into test1 values(2,'sam'); 1 row created. SQL> select * from test1;        EID ENAME ---------- ----------          1 dan          2 sam SQL> insert into test1 values(5,'sam'); insert into test1 values(5,'sam') * ERROR at line 1: ORA-02290: check constraint (SYSTEM.SYS_C007650) violated SQL> insert into test1 values(4,'sam'); 1 row created. SQL> select * from test1;        EID ENAME ---------- ----------          1 dan          2 sam          4 sam SQL> insert into test1 values(55,'sam'); insert into test1 values(55,'sam') * ERROR at line 1: ORA-02290

 Not Null Constraint: ====================   -Restricted nulls but accepting duplicates      -Not null an not be applied at table level ex:: create table test1(eid int not null,ename varchar2(10) not null); EX:: SQL> create table test1(eid int not null,ename varchar2(10) not null); Table created. SQL> insert into test1 values(10,'raja'); 1 row created. SQL> insert into test1 values(20,'dan'); 1 row created. SQL> select * from test1;        EID ENAME ---------- ----------         10 raja         20 dan SQL> insert into test1 values(null,'dan'); insert into test1 values(null,'dan')                          * ERROR at line 1: ORA-01400: cannot insert NULL into ("SYSTEM"."TEST1"."EID") SQL> insert into test1 values(10,null); insert into test1 values(10,null)                             * ERROR at line 1: ORA-01400: cannot insert NULL into ("SYSTEM"."TEST1"."ENAME") SQL> select *

Unique Constraint:: ================  -Restricted Duplicates values but accepting nulls into a column column level:: ============ >create table test1(sno int unique,name varchar2(10) unique); EX:: SQL> create table test1(eid int unique,ename varchar2(10) unique); Table created. SQL> insert into test1 values(10,'virat'); 1 row created. SQL> select * from test1;        EID ENAME ---------- ----------         10 virat SQL> insert into test1 values(10,'rohit'); insert into test1 values(10,'rohit') * ERROR at line 1: ORA-00001: unique constraint (SYSTEM.SYS_C007643) violated SQL> insert into test1 values(20,'virat'); insert into test1 values(20,'virat') * ERROR at line 1: ORA-00001: unique constraint (SYSTEM.SYS_C007644) violated SQL> insert into test1 values(20,'rohit'); 1 row created. SQL> select * from test1;        EID ENAME ---------- ----------         10 virat         20 rohit SQL> insert into test1(null,'