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1.7 alteR taBle
In Structured Query Language, the ALTER TABLE statement allows you to add, modify, and delete columns from an existing
table. This statement also allows database administrators to add and remove SQL constraints from existing tables.
Syntax:
ALTER TABLE table_name
ADD column name datatype;
Example:
ALTER TABLE EmpLOyEE_DETAiLS
ADD Emp_iD varchar(5);
Output:
+-----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-------------+------+-----+---------+-------+
| Emp_NAmE | varchar(20) | yES | | NULL | |
| Emp_DEpARTmENT | varchar(20) | yES | | NULL | |
| Emp_DESiGNATiON | varchar(20) | yES | | NULL | |
| DATE_OF_BiRTH | date | yES | | NULL | |
| ADDRESS | varchar(20) | yES | | NULL | |
| Emp_iD | varchar(5) | yES | | NULL | |
+-----------------+-------------+------+-----+---------+-------+
You can set a column as Primary Key with the following Command.
ALTER TABLE Table_Name
ADD pRimARy KEy (Column_Name);
Example:
ALTER TABLE EmpLOyEE_DETAiLS
ADD pRimARy KEy (Emp_iD);
Output:
+-----------------+-------------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-----------------+-------------+------+-----+---------+-------+
| Emp_NAmE | varchar(20) | yES | | NULL | |
| Emp_DEpARTmENT | varchar(20) | yES | | NULL | |
| Emp_DESiGNATiON | varchar(20) | yES | | NULL | |
| DATE_OF_BiRTH | date | yES | | NULL | |
| ADDRESS | varchar(20) | yES | | NULL | |
| Emp_iD | varchar(5) | NO | pRi | NULL | |
+-----------------+-------------+------+-----+---------+-------+
1.8 upDate taBle
UPDATE command is used to modify the existing records in a table.
Syntax:
UpDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
Example:
UpDATE EmpLOyEE_DETAiLS
SET EMP_ID = ′EMP05′ WHERE EMP_NAME = ′SOMNATH_PATRA′
Database Concepts—RDBMS Tool 173

