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。