Download alter table

Advanced Database
Management System
Lab no. 12
Outline
• SQL Commands (for MySQL)
– Alter Command
– phpMyAdmin (DB backup)
Alter table statement
• Changing a table name
– alter table table_name rename
new_table_name;
• Adding Columns
– alter table table_name add column
column_name column_attributes;
• Dropping Columns
– alter table table_name drop column
column_name;
Alter table statement
• You can add indexes using the index, unique, and primary
key commands in the same way you would use them in the
create statement:
• Adding index
– alter table my_table add index index_name (column_name1);
• Dropping Index
– alter table my_table drop index index_name;
• Adding unique index constraint
– alter table my_table add unique index_name(column_name);
– Note that unique index cannot be created on a column with duplicate
values
• Adding Unique constraint on a column
– alter table my_table add unique(column_name);
Alter table statement
• Adding primary key
– alter table my_table add primary key(my_column);
• Dropping primary key
– alter table my_table drop primary key;
Alter table statement
• Adding foreign key
– alter table my_table add foreign key (my_column)
references other_table(col);
• Dropping foreign key
– alter table my_table drop foriegn key;
Note:
– Other option to add foreign key from PHPMyAdmin
is shown in next slide
• You will have to create an index on the foreign key column
then select the option shown in next slide.
Alter cont’d
• Changing column definitions
– It is possible to change a column’s name or attributes with either
the change or modify command.
• To change a column’s name you must also redefine the
column’s attributes. The following will work:
– alter table my_table change old_col new_col int not null;
• To change a column’s characteristics/attributes, do the
following:
– alter table my_table modify col_name varchar(50);
For further reference on ALTER
http://dev.mysql.com/doc/refman/5.0/en/altertable.html
Show statement cont’d
• show columns
– Syntax: show columns from table_name;
• show index
– Syntax: show index from table_name;
• show table status
– Syntax: Show table status like ‘table_name’;
The Show statement
•
Show Database: On mySql console write…
– mysql> show databases;
•
Show Tables: On MySql console write…
– mysql> Use guestbook;
– mysql> show tables;
•
Example:
mysql> use guestbook;
Database changed
mysql> show tables;
+---------------------+
| Tables_in_guestbook |
+---------------------+
| guestbook
|
| guestbook1
|
| my_table
|
+---------------------+
3 rows in set (0.11 sec)
mysql>
Example
mysql> show table status like 'guestbook'
*************************** 1. row ***************************
Name: guestbook
Engine: InnoDB
Version: 10
Row_format: Compact
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 0
Data_free: 0
Auto_increment: NULL
Create_time: 2008-04-05 01:38:12
Update_time: NULL
Check_time: NULL
Collation: latin1_swedish_ci
Checksum: NULL
Create_options:
Comment: InnoDB free: 4096 kB
1 row in set (0.02 sec)
mysql>_
Show cont’d
• Show create table:
– Syntax: show create table guestbook
mysql> show create table guestbook
*************************** 1. row ***************************
Table: guestbook
Create Table: CREATE TABLE `guestbook` (
`name` varchar(40) default NULL,
`location` varchar(40) default NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1
1 row in set (0.00 sec)
mysql>
Taking Database Backup
Backing Up and Restoring Your MySQL Database - Backing Up and Restoring
Your Database with PHPMyAdmin
( Page 5 of 5 )
You can backup your database using PHPMyAdmin in just a few mouse clicks. First
head over to your database by clicking the database name in the list on the left of the
screen. Once you get to your database details, you should get a menu header for
your database which looks like so:
Click on Export. This will get you to a screen with the following options.
From here it's just a matter of clicking the right options and the 'Go' Button to get
your database dump. To save the backup file on your computer, click on the Save as
file option and the corresponding compression option to get the backup to download
to your system.
Restoring your Database via PHPMyAdmin
Restoring your database is as easy as backing it up. If you would like to rewrite the
backup over an existing database, click on the database name in the database list on
the left, click all the check boxes next to the table names and select Drop in the With
selected: drop down box.