DDL,Dml,Tcl Commands

DDL:

create command create is a DDL command used to create a table or a database.

Creating a Database

To create a database in RDBMS, create command create command is uses. Following is the Syntax, S yntax, create database database-name;

Example for Creating Database create database Test;

The above command will create a database named Test.

Creating a Table

create command create command is also used to create a table. e can s!eci"y names and dataty!es o" various columns along.Following is the Syntax, create table table-name { column-name1 datatype1, column-name2 datatype2, column-name3 datatype3, column-name4 datatype4 };

create table command will tell the database system s ystem to create a new table with given table name and column in"ormation.

Example for creating Table Table create table Student(id int, name varchar, age int);

The above command will create a new table Student  in database system with # columns, namely id, name and age.

alter command

alter  command is used "or alteration o" table structures. There are various uses o" alter  command, such as, •

to add a column to existing table

•

to rename any existing column

•

to change datatype of any column or to modify its size.

•

  alter  is

also used to drop a column.

 To Add Column to existing Table

$sing alter command we can add a column to an existing table. Following is the Syntax, alter table table-name add(column-name datatype);

%ere is an &xam!le "or this, alter table Student add(address char);

The above command will add a new column address to the Student  table

 To Add Multiple Column to existing Table

$sing alter command we can even add multi!le columns to an existing table. Following is the Syntax, alter table table-name add(column-name1 datatype1, column-name2 datatype2, column-name3 datatype3);

%ere is an &xam!le "or this, alter table Student add(ather!name varchar("#), m$ther!name varchar("#), d$b date);

The above command will add three new columns to the Student  table

 To Add column with Default alue

alter command can add a new column to an existing table with de"ault values. Following is the Syntax, alter table table-name add(column-name1 datatype1 default data);

%ere is an &xam!le "or this,

alter table Student add(d$b date deault %1!&an!''%);

The above command will add a new column with de"ault value to the Student  table

 To Modify an existing Column

alter command is used to modi"y data ty!e o" an existing column . Following is the Syntax, alter table table-name m$diy(column-name datatype);

%ere is an &xam!le "or this, alter table Student m$diy(address varchar(3#));

The above command will modi"y address column o" the Student table

 To !ename a column

$sing alter command you can rename an existing column. Following is the S yntax, alter table table-name rename $ld!c$lumn!name t$ c$lumn!name;

%ere is an &xam!le "or this, alter table Student rename address t$ $cati$n;

The above command will rename address column to Location.

 To Drop a Column

alter command is also used to dro! columns also. Following is the Syntax, alter table table-name dr$p(c$lumn!name);

%ere is an &xam!le "or this, alter table Student dr$p(address);

The above command will dro! address column "rom the Student table "#L $ueries to Truncate% Drop or !ename a Table truncate command

truncate command removes all records "rom a table. But this command will not destroy the table's structure. hen we a!!ly truncate command on a table its (rimary )ey is initiali*ed. Following is its Syntax, truncate  table table-name

%ere is an &xam!le ex!laining it.

truncate table Student;

The above +uery will delete all the records o" Student  table. truncate  command is di""erent "rom delete  command. delete command will delete all the rows "rom a table whereas truncate command reinitiali*es a table-li)e a newly created table. For eg. /" you have a table with 01 rows and an auto2increment !rimary )ey, i" you usedelete command to delete all the rows, it will delete all the rows, but will not initiali*e the !rimary )ey, hence i" you will insert any row a"ter using delete command, the auto2increment !rimary )e y will start "rom 00. But in case o" truncate command, !rimary )ey is reinitiali*ed.

drop command

drop +uery com!letely removes a table "rom database. This command will also destroy the table structure. Following is its Syntax, drop table table-name

%ere is an &xam!le ex!laining it. dr$p table Student;

The above +uery will delete the Student  table com!letely. /t can also be used on Databases. For &xam!le, to dro! a database,  dr$p database Test;

The above +uery will dro! a database named Test "rom the system.

rename $uery

rename command is used to rename a table. Following is its Syntax, rename table old-table-name t$ new-table-name

%ere is an &xam!le ex!laining it. rename table Student t$ Student!rec$rd;

The above +uery will rename Student  table to Student-record .

DML command

Data Mani!ulation Language -DML statements are used "or manag ing data in database. DML commands are not autocommitted. /t means changes made by DML command are not  !ermanent to database, it can be rolled bac).

&' ()"*!T command

/nsert command is used to insert data into a table. Following is its general syntax, INSERT int$ table-name values(data1,data2,)

Lets see an exam!le, 3onsider a table Student  with "ollowing "ields. S_id

S_Name

age

*+S-T int$ Student values(1#1,%.dam%,1/);

The above command will insert a record into Student  table. S_id &+&

S_Name Adam

age &,

*xample to (nsert )-LL alue to a column

Both the statements below will insert 4$LL value into age column o" the Student table. *+S-T int$ Student(id,name) values(1#2,%.le0%);

5r, *+S-T int$ Student values(1#2,%.le0%,null);

The above command will insert only two column value other column is set to null. S_id

S_Name

&+&

Adam

&+/

Alex

age &,

*xample to (nsert Default alue to a column *+S-T int$ Student values(1#3,%hris%,deault)

S_id

S_Name

&+&

Adam

&+/

Alex

&+0

chris

Su!!ose the age column o" student table has de"ault value o" 06.

age &,

&1

7lso, i" you run the below +uery, it will insert de"ault value into the age column, whatever the de"ault value may be. *+S-T int$ Student values(1#3,%hris%)

/' -2DAT* command

$!date command is used to u!date a row o" a table. Following is its general syntax, UPDATE table-name set c$lumn!name  value where condition ;

Lets see an exam!le, update Student set age1 here s5id1#2;

S_id

S_Name

age

&+&

Adam

&,

&+/

Alex

&3

&+0

chris

&1

*xample to -pdate multiple columns 678.T Student set s5name%.bhi%,age19 here s5id1#3;

The above command will u!date two columns o" a record. S_id

S_Name

age

&+&

Adam

&,

&+/

Alex

&3

&+0

Abhi

&4

0' Delete command

Delete command is used to delete data "rom a table. Delete command can also be used with condition to delete a !articular row. Following is its general syntax, DELETE r$m table-name;

*xample to Delete all !ecords from a Table 8T r$m Student;

The above command will delete all the records "rom Student  table.

*xample to Delete a particular !ecord from a Table

3onsider the "ollowing Student table S_id

S_Name

age

&+&

Adam

&,

&+/

Alex

&3

&+0

Abhi

&4

8T r$m Student here s5id1#3;

The above command will delete the record where s2id is 01# "rom Student  table. S_id

S_Name

age

&+&

Adam

&,

&+/

Alex

&3

 TCL command

Transaction 3ontrol Language-T3L commands are used to manage transactions in database.These are used to manage the changes made by DML statements. /t also allows statements to be grou!ed together into logical transactions.

Commit command

3ommit command is used to !ermanently save any transaaction into database. Following is 3ommit command's syntax, commit;

!ollbac5 command

This command restores the database to last commited state. /t is also use with save!oint command to 8um! to a save!oint in a transaction. Following is Rollbac) command's syntax, rollback  t$ savepoint-name;

"aepoint command

savepoint  command is used to tem!orarily save a transaction so that you can rollbac) to that  !oint whenever necessary.

Following is save!oint command's syntax, a!epoint savepoint-name;

*xample of "aepoint and !ollbac5

Following is the class table, ID

NAME

&

abhi

/

adam

1

alex

Lets use some S9L +ueries on the above table and see the results. *+S-T int$ class values(/,%-ahul%); c$mmit; 678.T class set name%abhi:it% here id%/%; savep$int  A ; *+S-T int$ class values(",%hris%); savep$int "; *+S-T int$ class values(9,%rav$%); savep$int #; ST < r$m class;

The resultant table will loo) li)e, ID

NAME

&

abhi

/

adam

1

alex

,

abhi6it

7

chris

4

brao

 4ow rollback  to savepoint B r$llbac= t$ ; ST < r$m class;

The resultant table will loo) li)e

ID

NAME

&

abhi

/

adam

1

alex

,

abhi6it

7

chris

 4ow rollback  to savepoint A r$llbac= t$ .; ST < r$m class;

The result table will loo) li)e ID

NAME

&

abhi

/

adam

1

alex

,

abhi6it