MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
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 syntax is
tbl_name
FROM db_namedb_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
Section 24.8, “Extensions to SHOW Statements”.
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 Section 13.1.18.6, “Silent Column Specification Changes”.
SHOW COLUMNS displays the
following values for each table column:
Field
The column name.
Type
The column data type.
Collation
The collation for nonbinary string columns, or
NULL for other columns. This value is
displayed only if you use the FULL
keyword.
Null
The column nullability. The value is YES
if NULL values can be stored in the
column, NO if not.
Key
Whether the column is indexed:
If Key is empty, the column either is
not indexed or is indexed only as a secondary column in
a multiple-column, nonunique index.
If Key is PRI, the
column is a PRIMARY KEY or is one of
the columns in a multiple-column PRIMARY
KEY.
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.)
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.
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.
Extra
Any additional information that is available about a given column. The value is nonempty in these cases:
Privileges
The privileges you have for the column. This value is
displayed only if you use the FULL
keyword.
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
Section 24.3.5, “The INFORMATION_SCHEMA COLUMNS Table”.
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 Section 13.8.1, “DESCRIBE Statement”.
The SHOW CREATE TABLE,
SHOW TABLE STATUS, and
SHOW INDEX statements also
provide information about tables. See Section 13.7.5, “SHOW Statements”.