Топ-100
 

SHOW FIELDS

RDBMS Type: MySQL
Topic

Syntax:
SHOW [EXTENDED] [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 EXTENDED keyword causes the output to include information
about hidden columns that MySQL uses internally and are not accessible
by users.

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
https://dev.mysql.com/doc/refman/8.0/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
https://dev.mysql.com/doc/refman/8.0/en/silent-column-changes.html.

SHOW COLUMNS displays the following values for each table column:

o Field

The name of the column.

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:

o auto_increment for columns that have the AUTO_INCREMENT attribute.

o on update CURRENT_TIMESTAMP for TIMESTAMP or DATETIME columns that
have the ON UPDATE CURRENT_TIMESTAMP attribute.

o VIRTUAL GENERATED or VIRTUAL STORED for generated columns.

o DEFAULT_GENERATED for columns that have an expression default
value.

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
https://dev.mysql.com/doc/refman/8.0/en/information-schema-columns-tabl
e.html. The extended information about hidden columns is available only
using SHOW EXTENDED COLUMNS; it cannot be obtained from the 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 https://dev.mysql.com/doc/refman/8.0/en/describe.html.

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

URL: https://dev.mysql.com/doc/refman/8.0/en/show-columns.html

Example