You can create one table from another by adding a
SELECT
statement at the end of
the CREATE TABLE
statement:
CREATE TABLEnew_tbl
SELECT * FROMorig_tbl
;
MySQL creates new columns for all elements in the
SELECT
. For example:
mysql>CREATE TABLE test (a INT NOT NULL AUTO_INCREMENT,
->PRIMARY KEY (a), KEY(b))
->ENGINE=MyISAM SELECT b,c FROM test2;
This creates a MyISAM
table with three
columns, a
, b
, and
c
. Notice that the columns from the
SELECT
statement are appended to
the right side of the table, not overlapped onto it. Take the
following example:
mysql>SELECT * FROM foo;
+---+ | n | +---+ | 1 | +---+ mysql>CREATE TABLE bar (m INT) SELECT n FROM foo;
Query OK, 1 row affected (0.02 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql>SELECT * FROM bar;
+------+---+ | m | n | +------+---+ | NULL | 1 | +------+---+ 1 row in set (0.00 sec)
For each row in table foo
, a row is inserted
in bar
with the values from
foo
and default values for the new columns.
In a table resulting from
CREATE TABLE ...
SELECT
, columns named only in the
CREATE TABLE
part come first.
Columns named in both parts or only in the
SELECT
part come after that. The
data type of SELECT
columns can
be overridden by also specifying the column in the
CREATE TABLE
part.
If any errors occur while copying the data to the table, it is automatically dropped and not created.
You can precede the SELECT
by
IGNORE
or
REPLACE
to indicate how to handle
rows that duplicate unique key values. With
IGNORE
, new rows that duplicate an existing
row on a unique key value are discarded. With
REPLACE
, new rows replace rows
that have the same unique key value. If neither
IGNORE
nor
REPLACE
is specified, duplicate
unique key values result in an error.
CREATE TABLE ...
SELECT
does not automatically create any indexes for
you. This is done intentionally to make the statement as
flexible as possible. If you want to have indexes in the created
table, you should specify these before the
SELECT
statement:
mysql> CREATE TABLE bar (UNIQUE (n)) SELECT n FROM foo;
Some conversion of data types might occur. For example, the
AUTO_INCREMENT
attribute is not preserved,
and VARCHAR
columns can become
CHAR
columns. Retrained
attributes are NULL
(or NOT
NULL
) and, for those columns that have them,
CHARACTER SET
, COLLATION
,
COMMENT
, and the DEFAULT
clause.
When creating a table with
CREATE
TABLE ... SELECT
, make sure to alias any function
calls or expressions in the query. If you do not, the
CREATE
statement might fail or result in
undesirable column names.
CREATE TABLE artists_and_works SELECT artist.name, COUNT(work.artist_id) AS number_of_works FROM artist LEFT JOIN work ON artist.id = work.artist_id GROUP BY artist.id;
You can also explicitly specify the data type for a generated column:
CREATE TABLE foo (a TINYINT NOT NULL) SELECT b+1 AS a FROM bar;
For CREATE TABLE
... SELECT
, if IF NOT EXISTS
is
given and the destination table already exists, the result is
version dependent. Before MySQL 5.5.6, MySQL handles the
statement as follows:
The table definition given in the
CREATE TABLE
part is ignored. No error occurs, even if the definition does not match that of the existing table. MySQL attempts to insert the rows from theSELECT
part anyway.If there is a mismatch between the number of columns in the table and the number of columns produced by the
SELECT
part, the selected values are assigned to the rightmost columns. For example, if the table containsn
columns and theSELECT
producesm
columns, wherem
<n
, the selected values are assigned to them
rightmost columns in the table. Each of the initialn
–m
columns is assigned its default value, either that specified explicitly in the column definition or the implicit column data type default if the definition contains no default. If theSELECT
part produces too many columns (m
>n
), an error occurs.If strict SQL mode is enabled and any of these initial columns do not have an explicit default value, the statement fails with an error.
The following example illustrates IF NOT
EXISTS
handling:
mysql>CREATE TABLE t1 (i1 INT DEFAULT 0, i2 INT, i3 INT, i4 INT);
Query OK, 0 rows affected (0.05 sec) mysql>CREATE TABLE IF NOT EXISTS t1 (c1 CHAR(10)) SELECT 1, 2;
Query OK, 1 row affected, 1 warning (0.01 sec) Records: 1 Duplicates: 0 Warnings: 0 mysql>SELECT * FROM t1;
+------+------+------+------+ | i1 | i2 | i3 | i4 | +------+------+------+------+ | 0 | NULL | 1 | 2 | +------+------+------+------+ 1 row in set (0.00 sec)
As of MySQL 5.5.6, handling of
CREATE
TABLE IF NOT EXISTS ... SELECT
statements was changed
for the case that the destination table already exists. This
change also involves a change in MySQL 5.1 beginning with
5.1.51.
Previously, for
CREATE TABLE IF NOT EXISTS ... SELECT
, MySQL produced a warning that the table exists, but inserted the rows and wrote the statement to the binary log anyway. By contrast,CREATE TABLE ... SELECT
(withoutIF NOT EXISTS
) failed with an error, but MySQL inserted no rows and did not write the statement to the binary log.MySQL now handles both statements the same way when the destination table exists, in that neither statement inserts rows or is written to the binary log. The difference between them is that MySQL produces a warning when
IF NOT EXISTS
is present and an error when it is not.
This change means that, for the preceding example, the
CREATE
TABLE IF NOT EXISTS ... SELECT
statement inserts
nothing into the destination table as of MySQL 5.5.6.
This change in handling of IF NOT EXISTS
results in an incompatibility for statement-based replication
from a MySQL 5.1 master with the original behavior and a MySQL
5.5 slave with the new behavior. Suppose that
CREATE
TABLE IF NOT EXISTS ... SELECT
is executed on the
master and the destination table exists. The result is that rows
are inserted on the master but not on the slave. (Row-based
replication does not have this problem.)
To address this issue, statement-based binary logging for
CREATE
TABLE IF NOT EXISTS ... SELECT
is changed in MySQL 5.1
as of 5.1.51:
If the destination table does not exist, there is no change: The statement is logged as is.
If the destination table does exist, the statement is logged as the equivalent pair of
CREATE TABLE IF NOT EXISTS
andINSERT ... SELECT
statements. (If theSELECT
in the original statement is preceded byIGNORE
orREPLACE
, theINSERT
becomesINSERT IGNORE
orREPLACE
, respectively.)
This change provides forward compatibility for statement-based replication from MySQL 5.1 to 5.5 because when the destination table exists, the rows will be inserted on both the master and slave. To take advantage of this compatibility measure, the 5.1 server must be at least 5.1.51 and the 5.5 server must be at least 5.5.6.
To upgrade an existing 5.1-to-5.5 replication scenario, upgrade the master first to 5.1.51 or higher. Note that this differs from the usual replication upgrade advice of upgrading the slave first.
A workaround for applications that wish to achieve the original
effect (rows inserted regardless of whether the destination
table exists) is to use
CREATE
TABLE IF NOT EXISTS
and
INSERT ...
SELECT
statements rather than
CREATE
TABLE IF NOT EXISTS ... SELECT
statements.
Along with the change just described, the following related
change was made: Previously, if an existing view was named as
the destination table for
CREATE
TABLE IF NOT EXISTS ... SELECT
, rows were inserted
into the underlying base table and the statement was written to
the binary log. As of MySQL 5.1.51 and 5.5.6, nothing is
inserted or logged.
To ensure that the binary log can be used to re-create the
original tables, MySQL does not permit concurrent inserts during
CREATE TABLE ...
SELECT
.