SQL DDL Commands - Data Definition Language

SQL DDL Commands - Data Definition Language

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DDL changes the structure of the table like creating a table, deleting a table, altering a table, etc.

All the command of DDL are auto-committed that means it permanently save all the changes in the database.

CREATE – It is used to create a new table in the database.

SYNTAX:

CREATE TABLE Table_Name (Column_Name DataType , ..........);

EXAMPLE:

CREATE TABLE STUDENT(Name VARCHAR2(20), Email VARCHAR2(100), DOB DATE);

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DROP – It is used to delete both the structure and record stored in the table.

               We can drop database and table.

SYNTAX:

DROP TABLE Table_Name;

DROP DATABASE Database_Name;

EXAMPLE:

DROP TABLE STUDENT;

DROP DATBASE MASTER;

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ALTER – It is used to alter the structure of the database. This change could be either to modify the characteristics of an existing attribute or probably to add a new attribute.

SYNTAX:

ALTER TABLE Table_Name ADD Column_Name Column-Definition;    

ALTER TABLE Table_Name MODIFY(Column_Definitions); 

EXAMPLE:

ALTER TABLE STUDENT ADD(ADDRESS VARCHAR2(20));  

ALTER TABLE STUDENT MODIFY (NAME VARCHAR2(20));

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TRUNCATE: It is used to delete all the rows from the table and free the space containing the table.

SYNTAX:

TRUNCATE TABLE Table_Name;

EXAMPLE:  

TRUNCATE TABLE STUDENT;

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