MySQL (C API)VC实例及代码下载

11.4. 通过SQL语句来更改用户的密码

修改别人的,需要sysadmin role

EXEC sp_password NULL, 'newpassword', 'User'

如果帐号为SA执行EXEC sp_password NULL, 'newpassword', sa

11.5. 怎么判断出一个表的哪些字段不允许为空？

select COLUMN_NAME from INFORMATION_SCHEMA.COLUMNS where IS_NULLABLE='NO' and TABLE_NAME=tablename

11.6. 怎么样在数据库里找到含有相同字段的表？

a. 查已知列名的情况

SELECT b.name as TableName,a.name as columnname

From syscolumns a INNER JOIN sysobjects b

ON a.id=b.id

AND b.type='U'

AND a.name='你的字段名字'

b. 未知列名查所有在不同表出现过的列名

Select o.name As tablename,s1.name As columnname

From syscolumns s1, sysobjects o

Where s1.id = o.id

And o.type = 'U'

And Exists (

Select 1 From syscolumns s2

Where s1.name = s2.name

And s1.id <> s2.id

)

11.7. 查询第xxx行数据

假设id是主键：

select *

from (select top xxx * from yourtable) aa

where not exists(select 1 from (select top xxx-1 * from yourtable) bb where aa.id=bb.id)

如果使用游标也是可以的

fetch absolute [number] from [cursor_name]

行数为绝对行数

11.8. SQL Server日期计算

a. 一个月的第一天

SELECT DATEADD(mm, DATEDIFF(mm,0,getdate()), 0)

b. 本周的星期一

SELECT DATEADD(wk, DATEDIFF(wk,0,getdate()), 0)

c. 一年的第一天

SELECT DATEADD(yy, DATEDIFF(yy,0,getdate()), 0)

d. 季度的第一天

SELECT DATEADD(qq, DATEDIFF(qq,0,getdate()), 0)

e. 上个月的最后一天

SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(mm,0,getdate()), 0))

f. 去年的最后一天

SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate()), 0))

g. 本月的最后一天

SELECT dateadd(ms,-3,DATEADD(mm, DATEDIFF(m,0,getdate())+1, 0))

h. 本月的第一个星期一

select DATEADD(wk, DATEDIFF(wk,0,

dateadd(dd,6-datepart(day,getdate()),getdate())

), 0)

i. 本年的最后一天

SELECT dateadd(ms,-3,DATEADD(yy, DATEDIFF(yy,0,getdate())+1, 0))。

12.1.获取表结构[把 'sysobjects' 替换 成 'tablename' 即可]

SELECT CASE IsNull(I.name, '')

When '' Then ''

Else '*'

End as IsPK,

Object_Name(A.id) as t_name,

A.name as c_name,

IsNull(SubString(M.text, 1, 254), '') as pbc_init,

T.name as F_DataType,

CASE IsNull(TYPEPROPERTY(T.name, 'Scale'), '')

WHEN '' Then Cast(A.prec as varchar)

ELSE Cast(A.prec as varchar) + ',' + Cast(A.scale as varchar)

END as F_Scale,

A.isnullable as F_isNullAble

FROM Syscolumns as A

JOIN Systypes as T

ON (A.xType = T.xUserType AND A.Id = Object_id('sysobjects') )

LEFT JOIN ( SysIndexes as I

JOIN Syscolumns as A1

ON ( I.id = A1.id and A1.id = object_id('sysobjects') and (I.status & 0x800) = 0x800 AND A1.colid <= I.keycnt) )

ON ( A.id = I.id AND A.name = index_col('sysobjects', I.indid, A1.colid) )

LEFT JOIN SysComments as M

ON ( M.id = A.cdefault and ObjectProperty(A.cdefault, 'IsConstraint') = 1 )

ORDER BY A.Colid ASC

12.2..提取数据库内所有表的字段详细说明的SQL语句

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'

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 object_name(a.id),a.colorder

12.3.快速获取表test的记录总数[对大容量表非常有效]

快速获取表test的记录总数:

select rows from sysindexes where id = object_id(‘test’) and indid in (0,1)

(T115)