数据字典实例详解（做一个简单的网页查询数据库）

数据字典可以帮助开发人员理解各个数据项目的类型、数值和它们与现实世界中的对象的关系。做数据库设计时数据字典是不可或缺的一部分，本文列出了几种常用数据的相关已有表获取数据字典的一些脚本，以下脚本仅仅测试了部分数据库版本，未必全部适配。

SqlServer2000：

select d.name as tname, 字段名 = a.name, 类型 = b.name, 长度 = columnproperty(a.id, a.name, 'PRECISION'), 小数位数 = isnull(columnproperty(a.id, a.name, 'Scale'),0), 允许空 = case when a.isnullable = 1 then '√' else '' end, 默认值 = isnull(e.text, ''), 字段说明 = isnull(g.[value], '') from syscolumns a left join systypes b on a.xtype = b.xusertype inner join sysobjects d on a.id = d.id and d.xtype = 'U' and d.name <> 'dtproperties' left join syscomments e on a.cdefault = e.id left join sysproperties g on a.id = g.id and a.colid = g.smallid order by a.id, a.colorder

SqlServer2005以上：

select d.name as tname, 字段名 = a.name, 类型 = b.name, 长度 = columnproperty(a.id, a.name, 'PRECISION'), 小数位数 = isnull(columnproperty(a.id, a.name, 'Scale'),0), 允许空 = case when a.isnullable = 1 then '√' else '' end, 默认值 = isnull(e.text, ''), 字段说明 = isnull(g.[value], '') from syscolumns a left join systypes b on a.xtype = b.xusertype inner join sysobjects d on a.id = d.id and d.xtype = 'U' and d.name <> 'dtproperties' left join syscomments e on a.cdefault = e.id left join sys.extended_properties g on a.id = g.major_id and a.colid = g.minor_id order by a.id, a.colorder

Oracle：

select a.table_name as tname, a.column_name as 字段名, a.data_type as 类型, a.data_length as 长度, case when a.data_scale = null then 0 else a.data_scale end as 小数位数, case when a.nullable = 'Y' then '√' else '' end as 允许空, a.data_default as 默认值, case when b.comments = null then '' else b.comments end as 字段说明 from user_tab_columns A left join user_col_comments B on A.table_name = B.table_name and A.column_name = B.column_name order by column_id

MySql：

select a.table_name as tname, a.column_name as 字段名, a.data_type as 类型, a.character_maximum_length as 长度, a.numeric_scale as 小数位数, case when a.is_nullable = 'YES' then '√' else '' end as 允许空, a.column_default as 默认值, column_comment as 字段说明 from information_schema.columns A order by ordinal_position

达梦6：

select d.name as tname, a.name as 字段名, a.TYPE as 类型, a.LENGTH as 长度, a.SCALE as 小数位数, case when a.NULLABLE = 'Y' then '√' else '' end as 允许空, isnull(a.DEFVAL, '') as 默认值, isnull(a.resvd5, '') as 字段说明 from SYSDBA.SYSCOLUMNS a inner join SYSDBA.SYSTABLES d on a.id = d.id and d.type = 'U' order by a.id, a.colid

达梦7：

select a.table_name as tname, a.column_name as 字段名, a.data_type as 类型, a.data_length as 长度, case when a.data_scale = null then 0 else a.data_scale end as 小数位数, case when a.nullable = 'Y' then '√' else '' end as 允许空, a.data_default as 默认值, case when b.comments = null then '' else b.comments end as 字段说明 from user_tab_columns A left join user_col_comments B on A.table_name = B.table_name and A.column_name = B.column_name order by column_id

人大金仓：

select a.table_name as tname, a.column_name as 字段名, a.data_type as 类型, a.data_length as 长度, case when a.data_scale = null then 0 else a.data_scale end as 小数位数, case when a.nullable = 'Y' then '√' else '' end as 允许空, a.data_default as 默认值, '' as 字段说明 --相关的字段说明没有找到怎么获取 from user_tab_columns A order by column_id

当前的数据库设计更倾向于直接在数据库里建数据字典表，就不存在数据库兼容适配的问题了。