MySQL中的CREATE TABLE LIKE和CREATE TABLE SELECT
- CREATE TABLE LIKE
- CREATE TABLE SELECT
CREATE TABLE LIKE
CREATE TABLE ... LIKE可以用来复制表结构，源表上的索引和约束也会复制。CREATE TABLE ... LIKE不能复制表数据。CREATE TABLE ... LIKE只能复制基表，不能复制视图。CREATE TABLE ... LIKE可以复制CHECK约束，但是复制后的约束名称是自动生成的。CREATE TABLE ... LIKE不能复制外键约束，也不会保留DATA DIRECTORY和INDEX DIRECTORY表创建参数。CREATE TABLE ... LIKE不会复制表的临时属性。要复制临时表请使用CREATE TEMPORARY TABLE LIKE。- 当源表被
LOCK TABLES锁定时，CREATE TABLE LIKE语句无法成功执行。
用法示例：
CREATE TABLE t1 LIKE t2;
CREATE TEMPORARY TABLE t1 LIKE t2;
CREATE TABLE SELECT
CREATE TABLE ... SELECT可以用来复制表结构，但不会复制索引（主键也不会）。CREATE TABLE ... SELECT可以复制表数据（可以通过WHERE过滤）。CREATE TABLE ... SELECT可以复制基表，也可以复制视图。CREATE TABLE ... SELECT不能复制外键约束。CREATE TABLE ... SELECT支持在建表时定义字段，从源表复制过来的不同名字段会作为新增字段，同名的字段则会被覆盖。CREATE TABLE ... SELECT支持在建表时为字段定义约束和索引。
用法示例：
CREATE TABLE t1 SELECT * FROM t2 where 1=2; --仅复制表结构
CREATE TABLE t1 SELECT * FROM t2; --复制全量数据
CREATE TABLE t1 SELECT name,age FROM t2 where age>30; --复制部分数据--复制另外两张表关联查询的结果集
CREATE TABLE t1SELECT artist.name, COUNT(work.artist_id) AS number_of_worksFROM artist LEFT JOIN work ON artist.id = work.artist_idGROUP BY artist.id;--复制的列作为新增字段
CREATE TABLE t1 (a int) SELECT name,age FROM t2; --复制的不同列作为新增字段，同名的列被覆盖
CREATE TABLE t1 (a int, name varchar(30)) SELECT name,age FROM t2; --为复制过来的字段定义索引和约束
CREATE TABLE t1 (name varchar(30) not null) SELECT name,age FROM t2;
CREATE TABLE t1 (unique(employee_id)) SELECT employee_id,name FROM t3;
实验：
SQL> create table t2 (name varchar(30), age int not null);
SQL> create table t3 (employ_id int, name varchar(30), age int);
SQL> insert into t2 values ('Joe',35),('Rachel',31),('Monica',33);
SQL> insert into t3 values (11,'MJoe',35),(12,'MRachel',31),(13,'MMonica',33);
SQL> commit;SQL> select * from t2;
+--------+-----+
| name | age |
+--------+-----+
| Joe | 35 |
| Rachel | 31 |
| Monica | 33 |
+--------+-----+
3 rows in set (0.00 sec)SQL> select * from t3;
+-----------+---------+------+
| employ_id | name | age |
+-----------+---------+------+
| 11 | MJoe | 35 |
| 12 | MRachel | 31 |
| 13 | MMonica | 33 |
+-----------+---------+------+
3 rows in set (0.00 sec)--仅复制表结构
SQL> CREATE TABLE t1 SELECT * FROM t2 where 1=2;
Query OK, 0 rows affected (0.11 sec)
Records: 0 Duplicates: 0 Warnings: 0SQL> select * from t1;
Empty set (0.00 sec)SQL> desc t1;
+-----------+-----------------+------+-----+---------+--------------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------------+------+-----+---------+--------------------------+
| my_row_id | bigint unsigned | NO | PRI | NULL | auto_increment INVISIBLE |
| name | varchar(30) | YES | | NULL | |
| age | int | NO | | NULL | |
+-----------+-----------------+------+-----+---------+--------------------------+
3 rows in set (0.00 sec)--复制的列作为新增字段
SQL> CREATE TABLE t1 (a int) SELECT name,age FROM t2;
Query OK, 3 rows affected (0.07 sec)
Records: 3 Duplicates: 0 Warnings: 0SQL> select * from t1;
+------+--------+-----+
| a | name | age |
+------+--------+-----+
| NULL | Joe | 35 |
| NULL | Rachel | 31 |
| NULL | Monica | 33 |
+------+--------+-----+
3 rows in set (0.00 sec)--复制的不同列作为新增字段，同名的列被覆盖
SQL> CREATE TABLE t1 (a int, name varchar(30)) SELECT name,age FROM t2;
Query OK, 3 rows affected (0.07 sec)
Records: 3 Duplicates: 0 Warnings: 0SQL> select * from t1;
+------+--------+-----+
| a | name | age |
+------+--------+-----+
| NULL | Joe | 35 |
| NULL | Rachel | 31 |
| NULL | Monica | 33 |
+------+--------+-----+
3 rows in set (0.00 sec)--为复制过来的字段定义约束
SQL> CREATE TABLE t1 (name varchar(40) not null default 'Tony') SELECT name,age FROM t2;
Query OK, 3 rows affected (0.13 sec)
Records: 3 Duplicates: 0 Warnings: 0SQL> desc t1;
+-----------+-----------------+------+-----+---------+--------------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------------+------+-----+---------+--------------------------+
| my_row_id | bigint unsigned | NO | PRI | NULL | auto_increment INVISIBLE |
| name | varchar(40) | NO | | Tony | |
| age | int | NO | | NULL | |
+-----------+-----------------+------+-----+---------+--------------------------+
3 rows in set (0.00 sec)--为复制过来的字段定义索引
SQL> CREATE TABLE t1 (unique(employ_id)) SELECT employ_id,name FROM t3;
Query OK, 3 rows affected (0.07 sec)
Records: 3 Duplicates: 0 Warnings: 0SQL> desc t1;
+-----------+-----------------+------+-----+---------+--------------------------+
| Field | Type | Null | Key | Default | Extra |
+-----------+-----------------+------+-----+---------+--------------------------+
| my_row_id | bigint unsigned | NO | PRI | NULL | auto_increment INVISIBLE |
| employ_id | int | YES | UNI | NULL | |
| name | varchar(30) | YES | | NULL | |
+-----------+-----------------+------+-----+---------+--------------------------+
3 rows in set (0.01 sec)
References
【1】https://dev.mysql.com/doc/refman/8.0/en/create-table-select.html
【2】https://dev.mysql.com/doc/refman/8.0/en/create-table-like.html
