13.1.18.4 CREATE TABLE ... SELECT Statement
You can create one table from another by adding a SELECT
statement at the end of the CREATE TABLE
statement:
CREATE TABLE new_tbl [AS] SELECT * FROM orig_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
. The ENGINE
option is part of the CREATE TABLE
statement, and should not be used following the SELECT
; this would result in a syntax error. The same is true for other CREATE TABLE
options such as CHARSET
.
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
, 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. For more information, see Comparison of the IGNORE Keyword and Strict SQL Mode.
Because the ordering of the rows in the underlying SELECT
statements cannot always be determined, CREATE TABLE ... IGNORE SELECT
and CREATE TABLE ... REPLACE SELECT
statements are flagged as unsafe for statement-based replication. Such statements produce a warning in the error log when using statement-based mode and are written to the binary log using the row-based format when using MIXED
mode. See also Section 16.2.1.1, “Advantages and Disadvantages of Statement-Based and Row-Based Replication”.
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;
For CREATE TABLE ... SELECT
, the destination table does not preserve information about whether columns in the selected-from table are generated columns. The SELECT
part of the statement cannot assign values to generated columns in the destination table.
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 column in the created table:
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 target table exists, nothing is inserted into the destination table, and the statement is not 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
.
You cannot use FOR UPDATE
as part of the SELECT
in a statement such as CREATE TABLE
. If you attempt to do so, the statement fails. new_table
SELECT ... FROM old_table
...