GBase 8a数据库集群支持表的注释comment ,字段的注释,本文介绍表创建时的注释以及表注释和字段注释的装修。
目录导航
建表
在建表语句里,直接在字段和表定义后面,加上comment 关键字,后面加上字符串即可。
根据现有规定,comment的最大长度是2000个字符。
gbase> create table testcomment(id int comment '编号', name varchar(100) comment '姓名') comment '测试注释';
Query OK, 0 rows affected (Elapsed: 00:00:00.29)
gbase> show create table testcomment;
+-------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| testcomment | CREATE TABLE "testcomment" (
"id" int(11) DEFAULT NULL COMMENT '编号',
"name" varchar(100) DEFAULT NULL COMMENT '姓名'
) ENGINE=EXPRESS DEFAULT CHARSET=utf8 TABLESPACE='sys_tablespace' COMMENT='测试注释' |
+-------------+-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (Elapsed: 00:00:00.00)
gbase>
更改表注释
用alter table TABLENAME comment '新的注释内容’对表的注释进行修改。
gbase> alter table testcomment comment '测试表注释修改';
Query OK, 0 rows affected (Elapsed: 00:00:00.12)
gbase> show create table testcomment;
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| testcomment | CREATE TABLE "testcomment" (
"id" int(11) DEFAULT NULL COMMENT '编号',
"name" varchar(100) DEFAULT NULL COMMENT '姓名'
) ENGINE=EXPRESS DEFAULT CHARSET=utf8 TABLESPACE='sys_tablespace' COMMENT='测试表注释修改' |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (Elapsed: 00:00:00.00)
更改列注释
用alter table TABLENAME modify 列名字 列定义 comment进行修改。
注意列的原有定义要保持,包括类型,NOT NULL, default等。
gbase> alter table testcomment modify id int comment '测试编号修改';
Query OK, 0 rows affected (Elapsed: 00:00:00.14)
Records: 0 Duplicates: 0 Warnings: 0
gbase> show create table testcomment;
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| testcomment | CREATE TABLE "testcomment" (
"id" int(11) DEFAULT NULL COMMENT '测试编号修改',
"name" varchar(100) DEFAULT NULL COMMENT '姓名'
) ENGINE=EXPRESS DEFAULT CHARSET=utf8 TABLESPACE='sys_tablespace' COMMENT='测试表注释修改' |
+-------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (Elapsed: 00:00:00.00)
添加注释
添加注释和修改定时完全一样的操作。
gbase> desc t1;
+-------+----------+------+-----+---------+-------+
| Field | Type | Null | Key | Default | Extra |
+-------+----------+------+-----+---------+-------+
| id | int(11) | YES | MUL | NULL | |
| value | int(11) | YES | | NULL | |
| birth | datetime | YES | | NULL | |
+-------+----------+------+-----+---------+-------+
3 rows in set (Elapsed: 00:00:00.01)
gbase> alter table t1 comment '添加数值';
Query OK, 0 rows affected (Elapsed: 00:00:00.15)
gbase> show create table t1;
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1 | CREATE TABLE "t1" (
"id" int(11) DEFAULT NULL,
"value" int(11) DEFAULT NULL,
"birth" datetime DEFAULT NULL,
KEY "idx_id" ("id") KEY_BLOCK_SIZE=4096 USING HASH GLOBAL
) ENGINE=EXPRESS DEFAULT CHARSET=utf8 TABLESPACE='sys_tablespace' COMMENT='添加数值' |
+-------+------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (Elapsed: 00:00:00.00)
gbase> alter table t1 modify id int comment '添加注释';
Query OK, 0 rows affected (Elapsed: 00:00:00.16)
Records: 0 Duplicates: 0 Warnings: 0
gbase> show create table t1;
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Table | Create Table |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| t1 | CREATE TABLE "t1" (
"id" int(11) DEFAULT NULL COMMENT '添加注释',
"value" int(11) DEFAULT NULL,
"birth" datetime DEFAULT NULL,
KEY "idx_id" ("id") KEY_BLOCK_SIZE=4096 USING HASH GLOBAL
) ENGINE=EXPRESS DEFAULT CHARSET=utf8 TABLESPACE='sys_tablespace' COMMENT='添加数值' |
+-------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
1 row in set (Elapsed: 00:00:00.00)