How to Use the MySQL alter statement

To learn how to use MySQL databases, you must first understand the usage of various statements. The following describes how to use MySQL alter statements. If you are not familiar with MySQL alter statements, I believe that you can have a clear understanding of the use of MySQL alter statements.

// Primary key

Alter table tabelname add new_field_id int (5) unsigned default 0 not null auto_increment, add primary key (new_field_id );
// Add a new column

Alter table t2 add d timestamp;
Alter table infos add ex tinyint not null default '0 ';
// Delete a column

Alter table t2 drop column c;
// Rename a column

Alter table t1 change a B integer;

// Change the column type

Alter table t1 change B bigint not null;
Alter table infos change list tinyint not null default '0 ';

// Rename the table

Alter table t1 rename t2;
Add Index

Mysql> alter table tablename change depno int (5) not null;
Mysql> alter table tablename add index name (field name 1 [, field name 2…]);
Mysql> alter table tablename add index emp_name (name );
Index with primary keywords

Mysql> alter table tablename add primary key (id );
Add an index with unique conditions

Mysql> alter table tablename add unique emp_name2 (cardnumber );
Delete An index

Mysql> alter table tablename drop index emp_name;
Modify Table:

Add field:

Mysql> alter table table_name ADD field_name field_type;
Modify the original field name and type:

Mysql> alter table table_name CHANGE old_field_name new_field_name field_type;
Delete field:

Mysql> alter table table_name DROP field_name;

The preceding section describes how to use the MySQL alter statement.

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