Rechercher dans le manuel MySQL
13.1.9.3 ALTER TABLE Examples
Begin with a table t1
created as shown here:
To rename the table from t1
to
t2
:
To change column a
from
INTEGER
to TINYINT NOT
NULL
(leaving the name the same), and to change column
b
from CHAR(10)
to
CHAR(20)
as well as renaming it from
b
to c
:
To add a new TIMESTAMP
column
named d
:
To add an index on column d
and a
UNIQUE
index on column a
:
To remove column c
:
To add a new AUTO_INCREMENT
integer column
named c
:
We indexed c
(as a PRIMARY
KEY
) because AUTO_INCREMENT
columns
must be indexed, and we declare c
as
NOT NULL
because primary key columns cannot
be NULL
.
For NDB
tables, it is also possible
to change the storage type used for a table or column. For
example, consider an NDB
table
created as shown here:
- Query OK, 0 rows affected (1.27 sec)
To convert this table to disk-based storage, you can use the
following ALTER TABLE
statement:
- Query OK, 0 rows affected (2.99 sec)
- *************************** 1. row ***************************
- Table: t1
- ) /*!50100 TABLESPACE ts_1 STORAGE DISK */
It is not necessary that the tablespace was referenced when the
table was originally created; however, the tablespace must be
referenced by the ALTER TABLE
:
- Query OK, 0 rows affected (1.00 sec)
- ERROR 1005 (HY000): Can't create table 'c.#sql-1750_3' (errno: 140)
- Query OK, 0 rows affected (3.42 sec)
- *************************** 1. row ***************************
- Table: t1
- ) /*!50100 TABLESPACE ts_1 STORAGE DISK */
To change the storage type of an individual column, you can use
ALTER TABLE ... MODIFY [COLUMN]
. For example,
suppose you create an NDB Cluster Disk Data table with two
columns, using this CREATE TABLE
statement:
- Query OK, 0 rows affected (1.34 sec)
To change column c2
from disk-based to
in-memory storage, include a STORAGE MEMORY clause in the column
definition used by the ALTER TABLE statement, as shown here:
- Query OK, 0 rows affected (3.14 sec)
You can make an in-memory column into a disk-based column by
using STORAGE DISK
in a similar fashion.
Column c1
uses disk-based storage, since this
is the default for the table (determined by the table-level
STORAGE DISK
clause in the
CREATE TABLE
statement). However,
column c2
uses in-memory storage, as can be
seen here in the output of SHOW CREATE
TABLE
:
- *************************** 1. row ***************************
- Table: t3
When you add an AUTO_INCREMENT
column, column
values are filled in with sequence numbers automatically. For
MyISAM
tables, you can set the first sequence
number by executing SET
INSERT_ID=
before
value
ALTER TABLE
or by using the
AUTO_INCREMENT=
table option.
value
With MyISAM
tables, if you do not change the
AUTO_INCREMENT
column, the sequence number is
not affected. If you drop an AUTO_INCREMENT
column and then add another AUTO_INCREMENT
column, the numbers are resequenced beginning with 1.
When replication is used, adding an
AUTO_INCREMENT
column to a table might not
produce the same ordering of the rows on the slave and the
master. This occurs because the order in which the rows are
numbered depends on the specific storage engine used for the
table and the order in which the rows were inserted. If it is
important to have the same order on the master and slave, the
rows must be ordered before assigning an
AUTO_INCREMENT
number. Assuming that you want
to add an AUTO_INCREMENT
column to the table
t1
, the following statements produce a new
table t2
identical to t1
but with an AUTO_INCREMENT
column:
This assumes that the table t1
has columns
col1
and col2
.
This set of statements will also produce a new table
t2
identical to t1
, with
the addition of an AUTO_INCREMENT
column:
To guarantee the same ordering on both master and slave,
all columns of t1
must
be referenced in the ORDER BY
clause.
Regardless of the method used to create and populate the copy
having the AUTO_INCREMENT
column, the final
step is to drop the original table and then rename the copy:
Traduction non disponible
Le manuel MySQL n'est pas encore traduit en français sur l'infobrol. Seule la version anglaise est disponible pour l'instant.
Document créé le 26/06/2006, dernière modification le 26/10/2018
Source du document imprimé : https://www.gaudry.be/mysql-rf-alter-table-examples.html
L'infobrol est un site personnel dont le contenu n'engage que moi. Le texte est mis à disposition sous licence CreativeCommons(BY-NC-SA). Plus d'info sur les conditions d'utilisation et sur l'auteur.
Références
Ces références et liens indiquent des documents consultés lors de la rédaction de cette page, ou qui peuvent apporter un complément d'information, mais les auteurs de ces sources ne peuvent être tenus responsables du contenu de cette page.
L'auteur de ce site est seul responsable de la manière dont sont présentés ici les différents concepts, et des libertés qui sont prises avec les ouvrages de référence. N'oubliez pas que vous devez croiser les informations de sources multiples afin de diminuer les risques d'erreurs.