文章摘要
本文描述了一段SQL语句，用于从`sys.columns`表中提取和组织数据库的元数据，包括表结构（如表名、列名）、计算信息（如列宽度、精度）、约束信息（如是否为计算、是否为NOT NULL）、身份映射信息（如是否为IDENTITY字段）、排序信息、大小写信息、字符集信息、注释信息等。该SQL语句通过复杂的外联和连接操作，从多个表中提取信息，并根据表类型（如用户表、系统表、视图表）进行过滤。最终生成的视图用于集中管理数据库的元数据，便于后续的数据完整性检查、自动化维护等用途，同时确保元数据的准确性和一致性。
{OWNER, TABLE, S, COLUMN, DTTPCODE, LENGTH, SIZE, PREC, COMPUTE, NOTNULL, IDENTITY, DOMAIN, DEFAULT, ExtIdentitySeedInc, COMMENT,COLNNAME, ExtCollation, ExtIdtNotForReplication, ExtDeftConstName, ExtRowGuidCol}
select
u.name,
o.name,
c.column_id,
c.name,
case when c.system_type_id in (165, 167, 231) and c.max_length=-1 then t.name + ‘(Max)’ else t.name end,
c.precision,
case (c.max_length) when -1 then 0 else case when c.system_type_id in (99, 231, 239) then (c.max_length/2) else (c.max_length) end end as colnA,
c.scale,
case(c.is_computed) when 1 then convert(varchar(8000), (select z.definition from [%CATALOG%.]sys.computed_columns z where z.object_id=c.object_id and z.column_id=c.column_id)) else ” end as colnB,
case(c.is_nullable) when 1 then ‘NULL’ else ‘NOTNULL’ end,
case(c.is_identity) when 1 then ‘identity’ else ” end,
case when(c.user_type_id <> c.system_type_id) then (select d.name from [%CATALOG%.]sys.types d where d.user_type_id=c.user_type_id) else ” end as colnC,
convert(varchar(8000), d.definition),
case (c.is_identity) when 1 then convert(varchar, i.seed_value) + ‘, ‘ + convert(varchar, i.increment_value) else ” end as colnD,
convert(varchar(8000), p.value),
convert(varchar(8000), p.value),
c.collation_name,
case (i.is_not_for_replication) when 1 then ‘true’ else ‘false’ end,
d.name,
case(c.is_rowguidcol) when 1 then ‘true’ else ‘false’ end
from
[%CATALOG%.]sys.columns c
join [%CATALOG%.]sys.objects o on (o.object_id=c.object_id)
join [%CATALOG%.]sys.schemas u on (u.schema_id=o.schema_id)
join [%CATALOG%.]sys.types t on (t.user_type_id=c.system_type_id)
left outer join [%CATALOG%.]sys.identity_columns i on (i.object_id=c.object_id and i.column_id=c.column_id)
left outer join [%CATALOG%.]sys.default_constraints d on (d.object_id=c.default_object_id)
left outer join [%CATALOG%.]sys.extended_properties p on (p.major_id=o.object_id and p.minor_id=c.column_id and p.class=1)
where
o.type in (‘U’, ‘S’, ‘V’)
[ and u.name=%.q:OWNER%]
[ and o.name=%.q:TABLE%]
order by 1, 2, 3
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