SELECT (case when a.colorder=1 then d.name else '' end) N'表名', a.colorder N'字段序号', a.name N'字段名', (case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end) N'标识', (case when (SELECT count(*) FROM sysobjects WHERE (name in (SELECT name FROM sysindexes WHERE (id = a.id) AND (indid in (SELECT indid FROM sysindexkeys WHERE (id = a.id) AND (colid in (SELECT colid FROM syscolumns WHERE (id = a.id) AND (name = a.name))))))) AND (xtype = 'PK'))>0 then '√' else '' end) N'主键', b.name N'类型', a.length N'占用字节数', COLUMNPROPERTY(a.id,a.name,'PRECISION') as N'长度', isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0) as N'小数位数', (case when a.isnullable=1 then '√'else '' end) N'允许空', isnull(e.text,'') N'默认值', isnull(g.[value],'') AS N'字段说明' --into ##tx 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 where d.name='test1' order by object_name(a.id),a.colorder /* test1 1 colnull varchar 20 20 0 √ 2 col varchar 20 20 0 √ */从这个测试来看好像是一样的.
create database db1 go use db1 go select top 50000 id=identity(int,0,1),col2=null,col3='abc',col4='gif' into tb1 from sysobjects a,sysobjects b go create database db2 go use db2 go select top 50000 id=identity(int,0,1),col2='abc',col3='abc',col4='gif' into tb1 from sysobjects a,sysobjects b go --执行完毕后,查看两数据库属性,都为大小:2.73M,可用0.94M. /* drop table tb1 use db1 drop table tb1 use master drop database db1,db2 */
create table test1(colnull varchar(20),col varchar(20))
insert test1(col) values('')
/*
(1 行受影响)
*/
SELECT
(case when a.colorder=1 then d.name else '' end) N'表名',
a.colorder N'字段序号',
a.name N'字段名',
(case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end) N'标识',
(case when (SELECT count(*)
FROM sysobjects
WHERE (name in
(SELECT name
FROM sysindexes
WHERE (id = a.id) AND (indid in
(SELECT indid
FROM sysindexkeys
WHERE (id = a.id) AND (colid in
(SELECT colid
FROM syscolumns
WHERE (id = a.id) AND (name = a.name))))))) AND
(xtype = 'PK'))>0 then '√' else '' end) N'主键',
b.name N'类型',
a.length N'占用字节数',
COLUMNPROPERTY(a.id,a.name,'PRECISION') as N'长度',
isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0) as N'小数位数',
(case when a.isnullable=1 then '√'else '' end) N'允许空',
isnull(e.text,'') N'默认值',
isnull(g.[value],'') AS N'字段说明'
--into ##tx 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
where d.name='test1'
order by object_name(a.id),a.colorder
/*
test1 1 colnull varchar 20 20 0 √
2 col varchar 20 20 0 √
*/从这个测试来看好像是一样的.
go
use db1
go
select top 50000 id=identity(int,0,1),col2=null,col3='abc',col4='gif' into tb1 from sysobjects a,sysobjects b
go
create database db2
go
use db2
go
select top 50000 id=identity(int,0,1),col2='abc',col3='abc',col4='gif' into tb1 from sysobjects a,sysobjects b
go
--执行完毕后,查看两数据库属性,都为大小:2.73M,可用0.94M.
/*
drop table tb1
use db1
drop table tb1
use master
drop database db1,db2
*/
不定长的,null不占, null代表未分配地址。''已分配了地址。字段给''默认值与null比较, 这么一点空间的消耗比起性能的损失,算不了什么。 推荐尽可能使用默认值而不是null