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

262 Chapter 10 Working with Your MySQL Database
The different types of alterations you can make with this statement are shown in
Table 10.5.
Table 10.5 Possible Changes with the ALTER TABLE Statement
Syntax
Description
ADD [COLUMN] column_description Adds a new column in the specified location
[FIRST | AFTER column ]
(if not specified, then the column goes at the
end). Note that column_descriptions
need a name and a type, just as in a CREATE
statement.
ADD [COLUMN] (column_description, Adds one or more new columns at the end
column_description,...)
of the table.
ADD INDEX [index] (column,...) Adds an index to the table on the specified
column or columns.
ADD [CONSTRAINT [symbol]]
Makes the specified column or columns the
PRIMARY KEY (column,...)
primary key of the table.The CONSTRAINT
notation is for tables using foreign keys. See
Chapter 13”Advanced MySQL programming,”for
more details.
ADD UNIQUE [CONSTRAINT [symbol]] Adds a unique index to the table on the
[index] (column,...)
specified column or columns.The
CONSTRAINT notation is for InnoDB tables
using foreign keys. See Chapter 13 for more
details.
ADD [CONSTRAINT [symbol]]
Adds a foreign key to an InnoDB table.
FOREIGN KEY [index] (index_col,...) See Chapter 13 for more details.
[reference_definition]
ALTER [COLUMN] column {SET DEFAULT Adds or removes a default value for a
value | DROP DEFAULT}
particular column.
CHANGE [COLUMN] column new_column Changes the column called column so that it
description
has the description listed. Note that this syntax
can be used to change the name of a column
because a column_description
includes a name.
MODIFY [COLUMN] column_description Similar to CHANGE. Can be used to change
column types, not names.
DROP [COLUMN] column
Deletes the named column.
DROP PRIMARY KEY
Deletes the primary index (but not the
column).
DROP INDEX index
Deletes the named index.
DROP FOREIGN KEY key
Deletes the foreign key (but not the
column).