PHP and MySQL Web Development 4th Ed-tqw-_darksiderg

Altering Tables After Creation
263
Table 10.5
Syntax
DISABLE KEYS
ENABLE KEYS
RENAME [AS] new_table_name
ORDER BY col_name
CONVERT TO CHARACTER SET cs
COLLATE c
[DEFAULT] CHARACTER SET cs
COLLATE c
DISCARD TABLESPACE
IMPORT TABLESPACE
table_options
Possible Changes with the ALTER TABLE Statement
Description
Turns off index updating.
Turns on index updating.
Renames a table.
Re-creates the table with the rows in a particular
order. (Note that after you begin
changing the table, the rows will no longer
be in order.)
Converts all text-based columns to the
specified character set and collation.
Sets the default character set and collation.
Deletes the underlying tablespace file for an
InnoDB table. (See Chapter 13 for more
details on InnoDB.)
Re-creates the underlying tablespace file for
an InnoDB table. (See Chapter 13 for more
details on InnoDB.)
Allows you to reset the table options. Uses
the same syntax as CREATE TABLE.
Let’s look at a few of the more common uses of ALTER TABLE.
You may frequently realize that you haven’t made a particular column “big enough”
for the data it has to hold. For example, previously in the customers table, you allowed
names to be 50 characters long. After you start getting some data, you might notice that
some of the names are too long and are being truncated.You can fix this problem by
changing the data type of the column so that it is 70 characters long instead:
alter table customers
modify name char(70) not null;
Another common occurrence is the need to add a column. Imagine that a sales tax on
books is introduced locally and that Book-O-Rama needs to add the amount of tax to
the total order but keep track of it separately.You can add a tax column to the orders
table as follows:
alter table orders
add tax float(6,2) after amount;
Getting rid of a column is another case that comes up frequently.You can delete the column
you just added as follows:
alter table orders
drop tax;