Syntax:
SHOW [FULL] {COLUMNS | FIELDS}
    {FROM | IN} tbl_name
    [{FROM | IN} db_name]
    [LIKE 'pattern' | WHERE expr]

SHOW COLUMNS displays information about the columns in a given table.
It also works for views. SHOW COLUMNS displays information only for
those columns for which you have some privilege.

mysql> SHOW COLUMNS FROM City;
+-------------+----------+------+-----+---------+----------------+
| Field       | Type     | Null | Key | Default | Extra          |
+-------------+----------+------+-----+---------+----------------+
| ID          | int(11)  | NO   | PRI | NULL    | auto_increment |
| Name        | char(35) | NO   |     |         |                |
| CountryCode | char(3)  | NO   | MUL |         |                |
| District    | char(20) | NO   |     |         |                |
| Population  | int(11)  | NO   |     | 0       |                |
+-------------+----------+------+-----+---------+----------------+

An alternative to tbl_name FROM db_name syntax is db_name.tbl_name.
These two statements are equivalent:

SHOW COLUMNS FROM mytable FROM mydb;
SHOW COLUMNS FROM mydb.mytable;

The optional FULL keyword causes the output to include the column
collation and comments, as well as the privileges you have for each
column.

The LIKE clause, if present, indicates which column names to match. The
WHERE clause can be given to select rows using more general conditions,
as discussed in
http://dev.mysql.com/doc/refman/5.5/en/extended-show.html.

The data types may differ from what you expect them to be based on a
CREATE TABLE statement because MySQL sometimes changes data types when
you create or alter a table. The conditions under which this occurs are
described in
http://dev.mysql.com/doc/refman/5.5/en/silent-column-changes.html.

SHOW COLUMNS displays the following values for each table column:

o Field

  The column name.

o Type

  The column data type.

o Collation

  The collation for nonbinary string columns, or NULL for other
  columns. This value is displayed only if you use the FULL keyword.

o Null

  The column nullability. The value is YES if NULL values can be stored
  in the column, NO if not.

o Key

  Whether the column is indexed:

  o If Key is empty, the column either is not indexed or is indexed
    only as a secondary column in a multiple-column, nonunique index.

  o If Key is PRI, the column is a PRIMARY KEY or is one of the columns
    in a multiple-column PRIMARY KEY.

  o If Key is UNI, the column is the first column of a UNIQUE index. (A
    UNIQUE index permits multiple NULL values, but you can tell whether
    the column permits NULL by checking the Null field.)

  o If Key is MUL, the column is the first column of a nonunique index
    in which multiple occurrences of a given value are permitted within
    the column.

  If more than one of the Key values applies to a given column of a
  table, Key displays the one with the highest priority, in the order
  PRI, UNI, MUL.

  A UNIQUE index may be displayed as PRI if it cannot contain NULL
  values and there is no PRIMARY KEY in the table. A UNIQUE index may
  display as MUL if several columns form a composite UNIQUE index;
  although the combination of the columns is unique, each column can
  still hold multiple occurrences of a given value.

o Default

  The default value for the column. This is NULL if the column has an
  explicit default of NULL, or if the column definition includes no
  DEFAULT clause.

o Extra

  Any additional information that is available about a given column.
  The value is nonempty in these cases: auto_increment for columns that
  have the AUTO_INCREMENT attribute; on update CURRENT_TIMESTAMP for
  TIMESTAMP columns that have the ON UPDATE CURRENT_TIMESTAMP
  attribute.

o Privileges

  The privileges you have for the column. This value is displayed only
  if you use the FULL keyword.

o Comment

  Any comment included in the column definition. This value is
  displayed only if you use the FULL keyword.

Table column information is also available from the INFORMATION_SCHEMA
COLUMNS table. See
http://dev.mysql.com/doc/refman/5.5/en/columns-table.html.

You can list a table's columns with the mysqlshow db_name tbl_name
command.

The DESCRIBE statement provides information similar to SHOW COLUMNS.
See http://dev.mysql.com/doc/refman/5.5/en/describe.html.

The SHOW CREATE TABLE, SHOW TABLE STATUS, and SHOW INDEX statements
also provide information about tables. See [HELP SHOW].

URL: http://dev.mysql.com/doc/refman/5.5/en/show-columns.html

