精妙SQL語句收藏
新一篇: 對查詢的優化~ | 舊一篇: sql語句
查詢表内容
SELECT
表名=case when a.colorder=1 then d.name else '' end,
表說明=case when a.colorder=1 then isnull(f.value,'') else '' end,
字段序号=a.colorder,
字段名=a.name,
辨別=case when COLUMNPROPERTY( a.id,a.name,'IsIdentity')=1 then '√'else '' end,
主鍵=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,
類型=b.name,
占用位元組數=a.length,
長度=COLUMNPROPERTY(a.id,a.name,'PRECISION'),
小數位數=isnull(COLUMNPROPERTY(a.id,a.name,'Scale'),0),
允許空=case when a.isnullable=1 then '√'else '' end,
預設值=isnull(e.text,''),
字段說明=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='要查詢的表' --如果隻查詢指定表,加上此條件
order by a.id,a.colorder
========================================================
SQL交*表執行個體
很簡單的一個東西,見網上好多朋友問“怎麼實作交*表?”,以下是我寫的一個例子,資料庫基于SQL SERVER 2000。
建表:
在查詢分析器裡運作:
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'張三',N'國文',60)
INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'數學',70)
INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'英語',80)
INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'數學',75)
INSERT INTO [test] ([name],[subject],[Source]) values (N'王五',N'國文',57)
INSERT INTO [test] ([name],[subject],[Source]) values (N'李四',N'國文',80)
INSERT INTO [test] ([name],[subject],[Source]) values (N'張三',N'英語',100)
Go
交*表語句的實作:
--用于:交*表的列數是确定的
select name,sum(case subject when '數學' then source else 0 end) as '數學',
sum(case subject when '英語' then source else 0 end) as '英語',
sum(case subject when '國文' then source else 0 end) as '國文'
from test
group by name
--用于:交*表的列數是不确定的
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 存儲過程的分頁方案比拼
出處
SQL Server 存儲過程的分頁,這個問題已經讨論過幾年了,很多朋友在問我,是以在此發表一下我的觀點
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
插入資料:(2萬條,用更多的資料測試會明顯一些)
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
-------------------------------------
分頁方案一:(利用Not In和SELECT TOP分頁)
語句形式:
SELECT TOP 10 *
FROM TestTable
WHERE (ID NOT IN
(SELECT TOP 20 id
FROM TestTable
ORDER BY id))
ORDER BY ID
SELECT TOP 頁大小 *
FROM TestTable
WHERE (ID NOT IN
(SELECT TOP 頁大小*頁數 id
FROM 表
ORDER BY id))
ORDER BY ID
-------------------------------------
分頁方案二:(利用ID大于多少和SELECT TOP分頁)
語句形式:
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 頁大小 *
FROM TestTable
WHERE (ID >
(SELECT MAX(id)
FROM (SELECT TOP 頁大小*頁數 id
FROM 表
ORDER BY id) AS T))
ORDER BY ID
-------------------------------------
分頁方案三:(利用SQL的遊标存儲過程分頁)
create procedure XiaoZhengGe
@sqlstr nvarchar(4000), --查詢字元串
@currentpage int, --第N頁
@pagesize int --每頁行數
as
set nocount on
declare @P1 int, --P1是遊标的id
@rowcount int
exec sp_cursoropen @P1 output,@sqlstr,@scrollopt=1,@ccopt=1,@[email protected] output
select ceiling(1.0*@rowcount/@pagesize) as 總頁數--,@rowcount as 總行數,@currentpage as 目前頁
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:如果沒有主鍵,可以用臨時表,也可以用方案三做,但是效率會低。
建議優化的時候,加上主鍵和索引,查詢效率會提高。
通過SQL 查詢分析器,顯示比較:我的結論是:
分頁方案二:(利用ID大于多少和SELECT TOP分頁)效率最高,需要拼接SQL語句
分頁方案一:(利用Not In和SELECT TOP分頁) 效率次之,需要拼接SQL語句
分頁方案三:(利用SQL的遊标存儲過程分頁) 效率最差,但是最為通用
在實際情況中,要具體分析。