Скачать или смотреть Using MySQL Server 5.1 Alter Table, Truncate Table,Drop Table,Desc |Alter Table using MySQL 5.1

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Alter Table

Alter table query is used to modify structure of a table.
we can add, delete or modify column.

1.Adding New column in a Table
ALTER TABLE table_name
ADD column_name datatype;

Example:
Adding column grade in the table student

ALTER TABLE student
ADD grade varchar(2);

2.Dropping column from table

ALTER TABLE table_name
DROP COLUMN column_name;

Example:
Deleting column grade from the table student.

ALTER TABLE student
DROP COLUMN grade;

3.Modifying Column of a Table
ALTER TABLE table_name
MODIFY COLUMN column_name data_type;

Example:
Changing the data type and size of column roll_no of student table.

ALTER TABLE student
modify column roll_no varchar(4);

4.Rename

Alter table can also used to rename a table.

Syntax:
alter table table_name rename to new_table_name;

Example:
alter table student
rename to studentdata;

Truncate Table

This command is used to delete all the records from table

Syntax:
TRUNCATE TABLE table_name;

Example:
TRUNCATE TABLE studentnew;

DROP TABLE

DROP TABLE query is used to delete table permanently from the database.

Syntax:
drop table table_name;

Example:
drop table studentnew;

Desc

Desc query is used to display structure of table.
desc table_name;

Example:
desc student;