MySQL 表和列的注释
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像代码一样,可以为表以及表中的列添加注释,方便其他人知晓其功能。对于一些字段,在经过一定时间后,创建者未必也能想起其具体的含意,所以注释显得尤为重要。 注释的添加注释的添加是通过在定义表或列的时候在末尾加上 可以在创建表的时候为表和列添加相应的注释。 CREATE TABLE test_comment
(
id SERIAL PRIMARY KEY,
col1 INT comment ‘列的注释‘
)
comment ‘表的注释‘; 执行上面的语句后创建了一个名为 然后可通过 mysql> SHOW CREATE TABLE test_comment\G
*************************** 1. row ***************************
Table: test_comment
Create Table: CREATE TABLE `test_comment` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`col1` int(11) DEFAULT NULL COMMENT ‘列的注释‘,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT=‘表的注释‘
1 row in set (0.00 sec) 注释的查看除了
SHOW TABLE STATUS WHERE name=‘table_name‘; 以下是通过 mysql> SHOW TABLE STATUS WHERE name=‘test_comment‘\G
*************************** 1. row ***************************
Name: test_comment
Engine: InnoDB
Version: 10
Row_format: Dynamic
Rows: 0
Avg_row_length: 0
Data_length: 16384
Max_data_length: 0
Index_length: 16384
Data_free: 0
Auto_increment: 1
Create_time: 2019-05-11 15:41:01
Update_time: NULL
Check_time: NULL
Collation: utf8mb4_general_ci
Checksum: NULL
Create_options:
Comment: 表的注释
1 row in set (0.00 sec) 而通过 SHOW FULL COLUMNS FROM <tablename> 以下是通过 mysql>SHOW FULL COLUMNS FROM test_comment\G
*************************** 1. row ***************************
Field: id
Type: bigint(20) unsigned
Collation: NULL
Null: NO
Key: PRI
Default: NULL
Extra: auto_increment
Privileges: select,insert,update,references
Comment:
*************************** 2. row ***************************
Field: col1
Type: int(11)
Collation: NULL
Null: YES
Key:
Default: NULL
Extra:
Privileges: select,insert,update,references
Comment: 列的注释
2 rows in set (0.00 sec) 借助 INFORMATION_SCHEMA 中的表 也能查看表或列的注释。 比如查看表的注释: SELECT table_comment
FROM information_schema.tables
WHERE table_name = ‘test_comment‘; 执行结果: mysql> SELECT table_comment
-> FROM information_schema.tables
-> WHERE table_name = ‘test_comment‘;
+---------------+
| TABLE_COMMENT |
+---------------+
| 表的注释 |
+---------------+
1 row in set (0.01 sec) 查看列的注释: SELECT column_comment
FROM information_schema.columns
WHERE column_name = ‘col1‘; 执行结果: mysql> SELECT column_comment
-> FROM information_schema.columns
-> WHERE column_name = ‘col1‘;
+----------------+
| COLUMN_COMMENT |
+----------------+
| 列的注释 |
+----------------+
1 row in set (0.00 sec) 注释的更新对已经存在的表和列,可通过相应的更新修改操作来添加注释。 列注释的添加,更新
通过 mysql> ALTER TABLE test_comment CHANGE col1 col1 INT COMMENT ‘列的注释2‘;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 通过 mysql> ALTER TABLE test_comment MODIFY col1 INT COMMENT ‘列的注释2‘;
Query OK, 0 rows affected (0.02 sec)
Records: 0 Duplicates: 0 Warnings: 0 查看修改结果: mysql> SHOW CREATE TABLE test_comment\G
*************************** 1. row ***************************
Table: test_comment
Create Table: CREATE TABLE `test_comment` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`col1` int(11) DEFAULT NULL COMMENT ‘列的注释2‘,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT=‘表的注释‘
1 row in set (0.00 sec) 表注释的添加,更新通过 mysql> ALTER TABLE test_comment comment ‘表的注释2‘;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0 查看更新结果: mysql> SHOW CREATE TABLE test_comment\G
*************************** 1. row ***************************
Table: test_comment
Create Table: CREATE TABLE `test_comment` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`col1` int(11) DEFAULT NULL COMMENT ‘列的注释2‘,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci COMMENT=‘表的注释2‘
1 row in set (0.00 sec) 注释的删除更新注释时指定为空即可。 mysql> ALTER TABLE test_comment COMMENT ‘‘;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0
mysql> ALTER TABLE test_comment MODIFY col1 INT COMMENT ‘‘;
Query OK, 0 rows affected (0.01 sec)
Records: 0 Duplicates: 0 Warnings: 0 查看删除结果: mysql> SHOW CREATE TABLE test_comment\G
*************************** 1. row ***************************
Table: test_comment
Create Table: CREATE TABLE `test_comment` (
`id` bigint(20) unsigned NOT NULL AUTO_INCREMENT,
`col1` int(11) DEFAULT NULL,
PRIMARY KEY (`id`),
UNIQUE KEY `id` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_general_ci
1 row in set (0.00 sec) 相关资源 |
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