MySQL create table as與create table like對比，mysqlcreate

MySQL create table as與create table like對比，mysqlcreate

      在MySQL資料庫中，關於表的複製有多種方式，比如我們可以使用create table ..as .. ，也可以使用create table .. like ..方式。然而這2種不同的方式還是有些差異的，他的差異到底在哪裡呢，本文通過示範對此展開描述。

1、mysql sakila表上的結構

--actor表狀態robin@localhost[sakila]> show table status like 'actor'\G*************************** 1. row ***************************           Name: actor         Engine: InnoDB        Version: 10     Row_format: Compact           Rows: 200 Avg_row_length: 81    Data_length: 16384Max_data_length: 0   Index_length: 16384      Data_free: 0 Auto_increment: 201    Create_time: 2014-12-25 13:08:25    Update_time: NULL     Check_time: NULL      Collation: utf8_general_ci       Checksum: NULL Create_options:         Comment: 1 row in set (0.00 sec)--actor表索引robin@localhost[sakila]> show index from actor\G*************************** 1. row ***************************        Table: actor   Non_unique: 0     Key_name: PRIMARY Seq_in_index: 1  Column_name: actor_id    Collation: A  Cardinality: 200     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: *************************** 2. row ***************************        Table: actor   Non_unique: 1     Key_name: idx_actor_last_name Seq_in_index: 1  Column_name: last_name    Collation: A  Cardinality: 200     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: 2 rows in set (0.00 sec)--actor表結構robin@localhost[sakila]> desc actor;+-------------+----------------------+------+-----+-------------------+-----------------------------+| Field       | Type                 | Null | Key | Default           | Extra                       |+-------------+----------------------+------+-----+-------------------+-----------------------------+| actor_id    | smallint(5) unsigned | NO   | PRI | NULL              | auto_increment              || first_name  | varchar(45)          | NO   |     | NULL              |                             || last_name   | varchar(45)          | NO   | MUL | NULL              |                             || last_update | timestamp            | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |+-------------+----------------------+------+-----+-------------------+-----------------------------+4 rows in set (0.00 sec)

2、使用create table as方式複製表

robin@localhost[sakila]> create table actor_as as select * from actor;Query OK, 200 rows affected (0.06 sec)Records: 200  Duplicates: 0  Warnings: 0robin@localhost[sakila]> desc actor_as;+-------------+----------------------+------+-----+-------------------+-----------------------------+| Field       | Type                 | Null | Key | Default           | Extra                       |+-------------+----------------------+------+-----+-------------------+-----------------------------+| actor_id    | smallint(5) unsigned | NO   |     | 0                 |                             || first_name  | varchar(45)          | NO   |     | NULL              |                             || last_name   | varchar(45)          | NO   |     | NULL              |                             || last_update | timestamp            | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |+-------------+----------------------+------+-----+-------------------+-----------------------------+--從上面的結果可以看出新表缺少了key資訊，以及自增列屬性 auto_incrementrobin@localhost[sakila]> show table status like 'actor_as'\G*************************** 1. row ***************************           Name: actor_as         Engine: InnoDB        Version: 10     Row_format: Compact           Rows: 200 Avg_row_length: 81    Data_length: 16384Max_data_length: 0   Index_length: 0      Data_free: 0 Auto_increment: NULL    Create_time: 2015-01-19 10:42:53    Update_time: NULL     Check_time: NULL      Collation: utf8_general_ci       Checksum: NULL Create_options:         Comment: 1 row in set (0.00 sec)--從上面的表結構可以看出，表狀態與原表等同，僅僅是建立時間的差異，robin@localhost[sakila]> show index from actor_as \GEmpty set (0.00 sec)--從上面的查詢可以看出，新表沒有任何索引

3、使用create table like方式複製表

robin@localhost[sakila]> create table actor_like like actor;Query OK, 0 rows affected (0.01 sec)robin@localhost[sakila]> select count(*) from actor_like;+----------+| count(*) |+----------+|        0 |+----------+1 row in set (0.00 sec)--從上面的查詢可知，使用like方式沒有任何資料被複製到新表robin@localhost[sakila]> desc actor_like;+-------------+----------------------+------+-----+-------------------+-----------------------------+| Field       | Type                 | Null | Key | Default           | Extra                       |+-------------+----------------------+------+-----+-------------------+-----------------------------+| actor_id    | smallint(5) unsigned | NO   | PRI | NULL              | auto_increment              || first_name  | varchar(45)          | NO   |     | NULL              |                             || last_name   | varchar(45)          | NO   | MUL | NULL              |                             || last_update | timestamp            | NO   |     | CURRENT_TIMESTAMP | on update CURRENT_TIMESTAMP |+-------------+----------------------+------+-----+-------------------+-----------------------------+robin@localhost[sakila]> show index from actor_like\G*************************** 1. row ***************************        Table: actor_like   Non_unique: 0     Key_name: PRIMARY Seq_in_index: 1  Column_name: actor_id    Collation: A  Cardinality: 0     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: *************************** 2. row ***************************        Table: actor_like   Non_unique: 1     Key_name: idx_actor_last_name Seq_in_index: 1  Column_name: last_name    Collation: A  Cardinality: 0     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: 2 rows in set (0.00 sec)--從上面的表結構以及索引資訊可以看到，表除了沒有資料之外，結構被進行了完整複製--下面為like方式的表插入資料robin@localhost[sakila]> insert into actor_like select * from actor;Query OK, 200 rows affected (0.03 sec)Records: 200  Duplicates: 0  Warnings: 0robin@localhost[sakila]> show index from actor_like\G*************************** 1. row ***************************        Table: actor_like   Non_unique: 0     Key_name: PRIMARY Seq_in_index: 1  Column_name: actor_id    Collation: A  Cardinality: 200     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: *************************** 2. row ***************************        Table: actor_like   Non_unique: 1     Key_name: idx_actor_last_name Seq_in_index: 1  Column_name: last_name  -- Author: Leshami    Collation: A          -- Blog  : http://blog.csdn.net/leshami   Cardinality: 200     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: 2 rows in set (0.00 sec)--上面的查詢中新表的索引統計資訊被收集robin@localhost[sakila]> explain select * from actor where last_name like 'A%';+----+-------------+-------+-------+---------------------+---------------------+---------+------+------+-----------------------+| id | select_type | table | type  | possible_keys       | key                 | key_len | ref  | rows | Extra                 |+----+-------------+-------+-------+---------------------+---------------------+---------+------+------+-----------------------+|  1 | SIMPLE      | actor | range | idx_actor_last_name | idx_actor_last_name | 137     | NULL |    7 | Using index condition |+----+-------------+-------+-------+---------------------+---------------------+---------+------+------+-----------------------+1 row in set (0.00 sec)robin@localhost[sakila]> explain select * from actor_like where last_name like 'A%';+----+-------------+------------+-------+---------------------+---------------------+---------+------+------+-----------------------+| id | select_type | table      | type  | possible_keys       | key                 | key_len | ref  | rows | Extra                 |+----+-------------+------------+-------+---------------------+---------------------+---------+------+------+-----------------------+|  1 | SIMPLE      | actor_like | range | idx_actor_last_name | idx_actor_last_name | 137     | NULL |    7 | Using index condition |+----+-------------+------------+-------+---------------------+---------------------+---------+------+------+-----------------------+1 row in set (0.00 sec)--從上面的執行計畫可以看出，like方式建表與原表使用了相同的執行計畫

4、基於myisam引擎進行create table like方式複製

robin@localhost[sakila]> alter table actor_like engine=myisam;Query OK, 200 rows affected (0.03 sec)Records: 200  Duplicates: 0  Warnings: 0robin@localhost[sakila]> show table status like 'actor_like'\G*************************** 1. row ***************************           Name: actor_like         Engine: MyISAM        Version: 10     Row_format: Dynamic           Rows: 200 Avg_row_length: 25    Data_length: 5016Max_data_length: 281474976710655   Index_length: 7168      Data_free: 0 Auto_increment: 201    Create_time: 2015-01-19 11:19:55    Update_time: 2015-01-19 11:19:55     Check_time: 2015-01-19 11:19:55      Collation: utf8_general_ci       Checksum: NULL Create_options:         Comment: 1 row in set (0.00 sec)robin@localhost[sakila]> create table actor_like_isam like actor_like;Query OK, 0 rows affected (0.01 sec)robin@localhost[sakila]> insert into actor_like_isam select * from actor_like;Query OK, 200 rows affected (0.00 sec)Records: 200  Duplicates: 0  Warnings: 0robin@localhost[sakila]> insert into actor_like_isam select * from actor_like;Query OK, 200 rows affected (0.00 sec)Records: 200  Duplicates: 0  Warnings: 0robin@localhost[sakila]> show index from actor_like_isam\G*************************** 1. row ***************************        Table: actor_like_isam   Non_unique: 0     Key_name: PRIMARY Seq_in_index: 1  Column_name: actor_id    Collation: A  Cardinality: 200     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: *************************** 2. row ***************************        Table: actor_like_isam   Non_unique: 1     Key_name: idx_actor_last_name Seq_in_index: 1  Column_name: last_name    Collation: A  Cardinality: 100     Sub_part: NULL       Packed: NULL         Null:    Index_type: BTREE      Comment: Index_comment: 2 rows in set (0.00 sec)robin@localhost[sakila]> explain select * from actor_like_isam where last_name like 'A%';+----+-------------+-----------------+-------+---------------------+---------------------+---------+------+------+-----------------------+| id | select_type | table           | type  | possible_keys       | key                 | key_len | ref  | rows | Extra                 |+----+-------------+-----------------+-------+---------------------+---------------------+---------+------+------+-----------------------+|  1 | SIMPLE      | actor_like_isam | range | idx_actor_last_name | idx_actor_last_name | 137     | NULL |    6 | Using index condition |+----+-------------+-----------------+-------+---------------------+---------------------+---------+------+------+-----------------------+1 row in set (0.00 sec)--從上面的測試可以看出基於myisam引擎方式對原表結構也是使用完成複製方式

5、小結
a、create table like方式會完整地複製表結構，但不會插入資料，需要單獨使用insert into或load data方式載入資料
b、create table as  方式會部分複製表結構，完整保留資料
c、create table as select .. where 1=0 會複製部分表結構，但不複製資料。
d、如果啟用了gtid，create table as方式不被支援。收到ERROR 1786 (HY000): CREATE TABLE ... SELECT is forbidden when @@GLOBAL.ENFORCE_GTID_CONSISTENCY = 1.

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