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.colorderSqlServer2005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。