CREATE TABLE AS SELECT
语法说明
CREATE TABLE AS SELECT 命令通过复制 SELECT 查询中指定的现有表中的列定义和列数据来创建新表。然而，它不会复制原表的约束、索引、视图或其他非数据属性。
语法结构
> CREATE [TEMPORARY] TABLE [ IF NOT EXISTS ] table_name
[ (column_name [, ...] ) ] AS {query}
Query can be any select statement in MO syntax.
SELECT
[ALL | DISTINCT ]
select_expr [, select_expr] [[AS] alias] ...
[INTO variable [, ...]]
[FROM table_references
[WHERE where_condition]
[GROUP BY {col_name | expr | position}
[ASC | DESC]]
[HAVING where_condition]
[ORDER BY {col_name | expr | position}
[ASC | DESC]] [ NULLS { FIRST | LAST } ]
[LIMIT {[offset,] row_count | row_count OFFSET offset}]
语法释义
-
ALL：默认选项，表示返回所有匹配的行，包括重复行。
-
DISTINCT：表示只返回唯一的行，即去除重复行。
-
select_expr：表示要选择的列或表达式。
-
AS alias：为选择的列或表达式指定一个别名。
-
[INTO variable[, ...]：用于将查询结果存储在一个变量中，而不是返回给客户端。
-
[FROM table_references]：指定从哪个表或哪些表中检索数据。table_references 可以是一个表名，也可以是一个包含多个表的复杂表达式（如连接）。
-
[WHERE where_condition]：用于过滤结果集，只返回满足 where_condition 条件的行。
-
[GROUP BY {col_name | expr | position} [ASC | DESC]]：用于将结果集按照一个或多个列或表达式进行分组；ASC 和 DESC 用于指定分组内行的排序方式。
-
[HAVING where_condition]：在分组后对分组进行过滤。通常与 GROUP BY 一起使用，以过滤掉不满足条件的分组。
-
[ORDER BY {col_name | expr | position} [ASC | DESC] [NULLS {FIRST | LAST}]]：用于对结果集进行排序; ASC 和 DESC 用于指定排序方式。
-
[NULLS {FIRST | LAST}]：用于指定如何处理 NULL 值在排序中的位置。
-
[LIMIT {[offset,] row_count | row_count OFFSET offset}]：用于限制返回的行数。offset 指定从结果集的哪一行开始返回，0 为第一行。row_count 指定返回的行数。
权限
在 Matrixone 中，执行 CREATE TABLE AS SELECT 语句需要具有至少以下权限：
-
CREATE权限：用户需要具有创建表的权限，这可以通过CREATE权限来实现。 -
INSERT权限：由于CREATE TABLE AS SELECT语句将选择的数据插入到新表中，因此用户还需要具有向目标表插入数据的权限。这可以通过INSERT权限来实现。 -
SELECT权限：用户需要能够选择源数据表中的数据，因此需要具有 SELECT 权限。
如需了解更多权限相关的操作，请查看 Matrixone 权限分类列表和 grant 说明。
示例
- 示例 1
create table t1(a int default 123, b char(5));
INSERT INTO t1 values (1, '1'),(2,'2'),(0x7fffffff, 'max');
mysql> create table t2 as select *from t1;--整表复制
Query OK, 3 rows affected (0.02 sec)
mysql> desc t2;
+-------+---------+------+------+---------+-------+---------+
| Field | Type | Null | Key | Default | Extra | Comment |
+-------+---------+------+------+---------+-------+---------+
| a | INT(32) | YES | | 123 | | |
| b | CHAR(5) | YES | | NULL | | |
+-------+---------+------+------+---------+-------+---------+
2 rows in set (0.01 sec)
mysql> select * from t2;
+------------+------+
| a | b |
+------------+------+
| 1 | 1 |
| 2 | 2 |
| 2147483647 | max |
+------------+------+
3 rows in set (0.00 sec)
- 示例 2
create table t1(a int default 123, b char(5));
INSERT INTO t1 values (1, '1'),(2,'2'),(0x7fffffff, 'max');
mysql> CREATE table test as select a as alias_a from t1;--为选择列指定别名
Query OK, 3 rows affected (0.02 sec)
mysql> desc test;
+---------+---------+------+------+---------+-------+---------+
| Field | Type | Null | Key | Default | Extra | Comment |
+---------+---------+------+------+---------+-------+---------+
| alias_a | INT(32) | YES | | 123 | | |
+---------+---------+------+------+---------+-------+---------+
1 row in set (0.01 sec)
mysql> select * from test;
+------------+
| alias_a |
+------------+
| 1 |
| 2 |
| 2147483647 |
+------------+
3 rows in set (0.01 sec)
- 示例 3
create table t1(a int default 123, b char(5));
INSERT INTO t1 values (1, '1'),(2,'2'),(0x7fffffff, 'max');
mysql> create table t3 as select * from t1 where 1=2;--只复制字段，不复制数据
Query OK, 0 rows affected (0.01 sec)
mysql> desc t3;
+-------+---------+------+------+---------+-------+---------+
| Field | Type | Null | Key | Default | Extra | Comment |
+-------+---------+------+------+---------+-------+---------+
| a | INT(32) | YES | | 123 | | |
| b | CHAR(5) | YES | | NULL | | |
+-------+---------+------+------+---------+-------+---------+
2 rows in set (0.01 sec)
mysql> select * from t3;
Empty set (0.00 sec)
- 示例 4
create table t1(a int default 123, b char(5));
INSERT INTO t1 values (1, '1'),(2,'2'),(0x7fffffff, 'max');
mysql> CREATE table t4(n1 int unique) as select max(a) from t1;--以原表数据聚合值作为新表的列
Query OK, 1 row affected (0.03 sec)
mysql> desc t4;
+--------+---------+------+------+---------+-------+---------+
| Field | Type | Null | Key | Default | Extra | Comment |
+--------+---------+------+------+---------+-------+---------+
| n1 | INT(32) | YES | UNI | NULL | | |
| max(a) | INT(32) | YES | | NULL | | |
+--------+---------+------+------+---------+-------+---------+
2 rows in set (0.01 sec)
mysql> select * from t4;
+------+------------+
| n1 | max(a) |
+------+------------+
| NULL | 2147483647 |
+------+------------+
1 row in set (0.00 sec)
- 示例 5
create table t5(n1 int,n2 int,n3 int);
insert into t5 values(1,1,1),(1,1,1),(3,3,3);
mysql> create table t5_1 as select distinct n1 from t5;--去除重复行
Query OK, 2 rows affected (0.02 sec)
mysql> select * from t5_1;
+------+
| n1 |
+------+
| 1 |
| 3 |
+------+
2 rows in set (0.00 sec)
- 示例 6
create table t6(n1 int,n2 int,n3 int);
insert into t6 values(1,1,3),(2,2,2),(3,3,1);
mysql> create table t6_1 as select * from t6 order by n3;--对结果集进行排序
Query OK, 3 rows affected (0.01 sec)
mysql> select * from t6_1;
+------+------+------+
| n1 | n2 | n3 |
+------+------+------+
| 3 | 3 | 1 |
| 2 | 2 | 2 |
| 1 | 1 | 3 |
+------+------+------+
3 rows in set (0.01 sec)
- 示例 7
create table t7(n1 int,n2 int,n3 int);
insert into t7 values(1,1,3),(1,2,2),(2,3,1),(2,3,1),(3,3,1);
mysql> CREATE TABLE t7_1 AS SELECT n1 FROM t7 GROUP BY n1 HAVING count(n1)>1;--对结果集进行分组
Query OK, 2 rows affected (0.02 sec)
mysql>
mysql> select * from t7_1;
+------+
| n1 |
+------+
| 1 |
| 2 |
+------+
2 rows in set (0.01 sec)
- 示例 8
create table t8(n1 int,n2 int,n3 int);
insert into t8 values(1,1,1),(2,2,2),(3,3,3);
mysql> CREATE TABLE t8_1 AS SELECT * FROM t8 limit 1 offset 1;--指定从结果集的第二行开始返回，返回行数为 1
mysql> select * from t8_1;
+------+------+------+
| n1 | n2 | n3 |
+------+------+------+
| 2 | 2 | 2 |
+------+------+------+
1 row in set (0.00 sec)
- 示例 9
create table t9 (a int primary key, b varchar(5) unique key);
create table t9_1 (
a int primary key,
b varchar(5) unique,
c int ,
d int,
foreign key(c) references t9(a),
INDEX idx_d(d)
);
insert into t9 values (101,'abc'),(102,'def');
insert into t9_1 values (1,'zs1',101,1),(2,'zs2',102,1);
mysql> create table t9_2 as select * from t9_1;
mysql> show create table t9_1;
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t9_1 | CREATE TABLE `t9_1` (
`a` INT NOT NULL,
`b` VARCHAR(5) DEFAULT NULL,
`c` INT DEFAULT NULL,
`d` INT DEFAULT NULL,
PRIMARY KEY (`a`),
UNIQUE KEY `b` (`b`),
KEY `idx_d` (`d`),
CONSTRAINT `018f27eb-0b33-7289-a3c2-af479b1833b1` FOREIGN KEY (`c`) REFERENCES `t9` (`a`) ON DELETE RESTRICT ON UPDATE RESTRICT
) |
+-------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.01 sec)
mysql> show create table t9_2;--源表带约束或者索引，CTAS 创建的新表默认不会带有原表的约束和索引
+-------+-------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-------------------------------------------------------------------------------------------------------------------+
| t9_2 | CREATE TABLE `t9_2` (
`a` INT NOT NULL,
`b` VARCHAR(5) DEFAULT NULL,
`c` INT DEFAULT NULL,
`d` INT DEFAULT NULL
) |
+-------+-------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)
--如果希望新表带有原表带约束和索引，则可以在建表后添加
ALTER TABLE t9_2 ADD PRIMARY KEY (a);
ALTER TABLE t9_2 ADD UNIQUE KEY (b);
ALTER TABLE t9_2 ADD FOREIGN KEY (c) REFERENCES t9 (a);
ALTER TABLE t9_2 ADD INDEX idx_d3 (d);
mysql> show create table t9_2;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t9_2 | CREATE TABLE `t9_2` (
`a` INT NOT NULL,
`b` VARCHAR(5) DEFAULT NULL,
`c` INT DEFAULT NULL,
`d` INT DEFAULT NULL,
PRIMARY KEY (`a`),
UNIQUE KEY `b` (`b`),
KEY `idx_d3` (`d`),
CONSTRAINT `018f282d-4563-7e9d-9be5-79c0d0e8136d` FOREIGN KEY (`c`) REFERENCES `t9` (`a`) ON DELETE RESTRICT ON UPDATE RESTRICT
) |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (0.00 sec)