Data Definition Language (DDL) | Shalini Chauhan
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Data Definition Language (DDL)
Today we will discuss more about DDL commands-
a. CREATE It is used to create a new table in the database.
Syntax:
1. CREATE TABLE TABLE_NAME (COLUMN_NAME DATATYPES[,....]);
Example:
1. CREATE TABLE EMPLOYEE(Name VARCHAR2(20), Email VARCHAR2(100), DOB DATE);
b. DROP TABLE
Example
1. DROP TABLE EMPLOYEE;
c. 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:
To add a new column in the table
1. ALTER TABLE table_name ADD column_name COLUMN-definition;
To modify existing column in the table:
1. ALTER TABLE MODIFY(COLUMN DEFINITION....);
EXAMPLE
1. ALTER TABLE STU_DETAILS ADD(ADDRESS VARCHAR2(20));
2. ALTER TABLE STU_DETAILS MODIFY (NAME VARCHAR2(20));
d. TRUNCATE:
It is used to delete all the rows from the table and free the space containing the table.
Syntax:
1. TRUNCATE TABLE table_name;
Example:
1. TRUNCATE TABLE EMPLOYEE;
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