Syntax:
ALTER [ONLINE | OFFLINE] [IGNORE] TABLE tbl_name
    [alter_specification [, alter_specification] ...]
    [partition_options]

alter_specification:
    table_options
  | ADD [COLUMN] col_name column_definition
        [FIRST | AFTER col_name ]
  | ADD [COLUMN] (col_name column_definition,...)
  | ADD {INDEX|KEY} [index_name]
        [index_type] (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]] PRIMARY KEY
        [index_type] (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]]
        UNIQUE [INDEX|KEY] [index_name]
        [index_type] (index_col_name,...) [index_option] ...
  | ADD FULLTEXT [INDEX|KEY] [index_name]
        (index_col_name,...) [index_option] ...
  | ADD SPATIAL [INDEX|KEY] [index_name]
        (index_col_name,...) [index_option] ...
  | ADD [CONSTRAINT [symbol]]
        FOREIGN KEY [index_name] (index_col_name,...)
        reference_definition
  | ALTER [COLUMN] col_name {SET DEFAULT literal | DROP DEFAULT}
  | CHANGE [COLUMN] old_col_name new_col_name column_definition
        [FIRST|AFTER col_name]
  | MODIFY [COLUMN] col_name column_definition
        [FIRST | AFTER col_name]
  | DROP [COLUMN] col_name
  | DROP PRIMARY KEY
  | DROP {INDEX|KEY} index_name
  | DROP FOREIGN KEY fk_symbol
  | DISABLE KEYS
  | ENABLE KEYS
  | RENAME [TO|AS] new_tbl_name
  | ORDER BY col_name [, col_name] ...
  | CONVERT TO CHARACTER SET charset_name [COLLATE collation_name]
  | [DEFAULT] CHARACTER SET [=] charset_name [COLLATE [=] collation_name]
  | DISCARD TABLESPACE
  | IMPORT TABLESPACE
  | FORCE
  | ADD PARTITION (partition_definition)
  | DROP PARTITION partition_names
  | TRUNCATE PARTITION {partition_names | ALL}
  | COALESCE PARTITION number
  | REORGANIZE PARTITION [partition_names INTO (partition_definitions)]
  | ANALYZE PARTITION {partition_names | ALL}
  | CHECK PARTITION {partition_names | ALL}
  | OPTIMIZE PARTITION {partition_names | ALL}
  | REBUILD PARTITION {partition_names | ALL}
  | REPAIR PARTITION {partition_names | ALL}
  | PARTITION BY partitioning_expression
  | REMOVE PARTITIONING

index_col_name:
    col_name [(length)] [ASC | DESC]

index_type:
    USING {BTREE | HASH}

index_option:
    KEY_BLOCK_SIZE [=] value
  | index_type
  | WITH PARSER parser_name
  | COMMENT 'string'

table_options:
    table_option [[,] table_option] ...  (see CREATE TABLE options)

partition_options:
    (see CREATE TABLE options)

ALTER TABLE changes the structure of a table. For example, you can add
or delete columns, create or destroy indexes, change the type of
existing columns, or rename columns or the table itself. You can also
change characteristics such as the storage engine used for the table or
the table comment.

Following the table name, specify the alterations to be made. If none
are given, ALTER TABLE does nothing.

The syntax for many of the permissible alterations is similar to
clauses of the CREATE TABLE statement. See [HELP CREATE TABLE], for
more information.

table_options signifies table options of the kind that can be used in
the CREATE TABLE statement, such as ENGINE, AUTO_INCREMENT,
AVG_ROW_LENGTH, MAX_ROWS, or ROW_FORMAT. For a list of all table
options and a description of each, see [HELP CREATE TABLE]. However,
ALTER TABLE ignores the DATA DIRECTORY and INDEX DIRECTORY table
options.

Use of table options with ALTER TABLE provides a convenient way of
altering single table characteristics. For example, if t1 is currently
not an InnoDB table, this statement changes its storage engine to
InnoDB:

ALTER TABLE t1 ENGINE = InnoDB;

To change the InnoDB table to use compressed row-storage format:

ALTER TABLE t1 ROW_FORMAT = COMPRESSED;

To reset the current auto-increment value:

ALTER TABLE t1 AUTO_INCREMENT = 13;

To change the default table character set:

ALTER TABLE t1 CHARACTER SET = utf8;

To add (or change) a table comment:

ALTER TABLE t1 COMMENT = 'New table comment';

To verify that the table options were changed as you intend, use SHOW
CREATE TABLE.

partition_options signifies options that can be used with partitioned
tables for repartitioning, for adding, dropping, merging, and splitting
partitions, and for performing partitioning maintenance. It is possible
for an ALTER TABLE statement to contain a PARTITION BY or REMOVE
PARTITIONING clause in an addition to other alter specifications, but
the PARTITION BY or REMOVE PARTITIONING clause must be specified last
after any other specifications. The ADD PARTITION, DROP PARTITION,
COALESCE PARTITION, REORGANIZE PARTITION, ANALYZE PARTITION, CHECK
PARTITION, and REPAIR PARTITION options cannot be combined with other
alter specifications in a single ALTER TABLE, since the options just
listed act on individual partitions. For a list of partition options
and a description of each, see [HELP CREATE TABLE]. For additional
information, see
http://dev.mysql.com/doc/refman/5.5/en/alter-table-partition-operations
.html.

Some operations may result in warnings if attempted on a table for
which the storage engine does not support the operation. These warnings
can be displayed with SHOW WARNINGS. See [HELP SHOW WARNINGS].

For information on troubleshooting ALTER TABLE, see
http://dev.mysql.com/doc/refman/5.5/en/alter-table-problems.html.

URL: http://dev.mysql.com/doc/refman/5.5/en/alter-table.html

