精妙SQL语句收藏

精妙SQL语句收藏

新一篇: 对查询的优化~ | 旧一篇: sql语句

查询表内容

SELECT

表名=case when a.colorder=1 then d.name else '' end,

表说明=case when a.colorder=1 then isnull(f.value,'') else '' end,

字段序号=a.colorder,

字段名=a.name,

标识=case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end,

主键=case when exists(SELECT 1 FROM sysobjects where xtype='PK' and name in (

SELECT name FROM sysindexes WHERE indid in(

SELECT indid FROM sysindexkeys WHERE id = a.id AND colid=a.colid

))) then '√' else '' end,

类型=b.name,

占用字节数=a.length,

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

left join sysproperties f on d.id=f.id and f.smallid=0

--where d.name='要查询的表' --如果只查询指定表,加上此条件

order by a.id,a.colorder

========================================================

SQL交*表实例

很简单的一个东西，见网上好多朋友问“怎么实现交*表？”，以下是我写的一个例子，数据库基于SQL SERVER 2000。

建表：

在查询分析器里运行：

CREATE TABLE [Test] (

[id] [int] IDENTITY (1, 1) NOT NULL ,

[name] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,

[subject] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,

[Source] [numeric](18, 0) NULL

) ON [PRIMARY]

GO

INSERT INTO [test] ([name],[subject],[Source]) values (N'张三',N'语文',60)

INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'数学',70)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'英语',80)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'数学',75)

INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'语文',57)

INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'语文',80)

INSERT INTO [test] ([name],[subject],[Source]) values (N'张三',N'英语',100)

Go

交*表语句的实现：

--用于：交*表的列数是确定的

select name,sum(case subject when '数学' then source else 0 end) as '数学',

sum(case subject when '英语' then source else 0 end) as '英语',

sum(case subject when '语文' then source else 0 end) as '语文'

from test

group by name

--用于：交*表的列数是不确定的

declare @sql varchar(8000)

set @sql = 'select name,'

select @sql = @sql + 'sum(case subject when '''+subject+'''

then source else 0 end) as '''+subject+''','

from (select distinct subject from test) as a

select @sql = left(@sql,len(@sql)-1) + ' from test group by name'

exec(@sql)

go

================================================================================

SQL Server 存储过程的分页方案比拼

出处

SQL Server 存储过程的分页，这个问题已经讨论过几年了，很多朋友在问我，所以在此发表一下我的观点

建立表：

CREATE TABLE [TestTable] (

[ID] [int] IDENTITY (1, 1) NOT NULL ,

[FirstName] [nvarchar] (100) COLLATE Chinese_PRC_CI_AS NULL ,

[LastName] [nvarchar] (100) COLLATE Chinese_PRC_CI_AS NULL ,

[Country] [nvarchar] (50) COLLATE Chinese_PRC_CI_AS NULL ,

[Note] [nvarchar] (2000) COLLATE Chinese_PRC_CI_AS NULL

) ON [PRIMARY]

GO

插入数据：(2万条，用更多的数据测试会明显一些)

SET IDENTITY_INSERT TestTable ON

declare @i int

set @i=1

while @i<=20000

begin

insert into TestTable([id], FirstName, LastName, Country,Note) values(@i, 'FirstName_XXX','LastName_XXX','Country_XXX','Note_XXX')

set @[email protected]+1

end

SET IDENTITY_INSERT TestTable OFF

-------------------------------------

分页方案一：(利用Not In和SELECT TOP分页)

语句形式：

SELECT TOP 10 *

FROM TestTable

WHERE (ID NOT IN

(SELECT TOP 20 id

FROM TestTable

ORDER BY id))

ORDER BY ID

SELECT TOP 页大小 *

FROM TestTable

WHERE (ID NOT IN

(SELECT TOP 页大小*页数 id

FROM 表

ORDER BY id))

ORDER BY ID

-------------------------------------

分页方案二：(利用ID大于多少和SELECT TOP分页）

语句形式：

SELECT TOP 10 *

FROM TestTable

WHERE (ID >

(SELECT MAX(id)

FROM (SELECT TOP 20 id

FROM TestTable

ORDER BY id) AS T))

ORDER BY ID

SELECT TOP 页大小 *

FROM TestTable

WHERE (ID >

(SELECT MAX(id)

FROM (SELECT TOP 页大小*页数 id

FROM 表

ORDER BY id) AS T))

ORDER BY ID

-------------------------------------

分页方案三：(利用SQL的游标存储过程分页)

create procedure XiaoZhengGe

@sqlstr nvarchar(4000), --查询字符串

@currentpage int, --第N页

@pagesize int --每页行数

as

set nocount on

declare @P1 int, --P1是游标的id

@rowcount int

exec sp_cursoropen @P1 output,@sqlstr,@scrollopt=1,@ccopt=1,@[email protected] output

select ceiling(1.0*@rowcount/@pagesize) as 总页数--,@rowcount as 总行数,@currentpage as 当前页

set @currentpage=(@currentpage-1)*@pagesize+1

exec sp_cursorfetch @P1,16,@currentpage,@pagesize

exec sp_cursorclose @P1

set nocount off

其它的方案：如果没有主键，可以用临时表，也可以用方案三做，但是效率会低。

建议优化的时候，加上主键和索引，查询效率会提高。

通过SQL 查询分析器，显示比较：我的结论是:

分页方案二：(利用ID大于多少和SELECT TOP分页）效率最高，需要拼接SQL语句

分页方案一：(利用Not In和SELECT TOP分页) 效率次之，需要拼接SQL语句

分页方案三：(利用SQL的游标存储过程分页) 效率最差，但是最为通用

在实际情况中，要具体分析。