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SQL专栏

SQL数据库基础知识汇总

SQL数据库高级知识汇总

一、基础部分

1、创建数据库

CREATE DATABASE dbname

2、删除数据库


DROP DATABASE dbname

3、创建新表


CREATE TABLE tabname(
col1 type1 [not null] [primary key],
col2 type2 [not null],..
)

根据已有的表创建新表:


使用旧表创建新表
create table tab_new
as 
select 
col1,
col2…
from tab_old

4、删除新表


DROP TABLE tablename

5、增加一个列


Alter table tabname add column col type

6、添加主键:


Alter table tabname add primary key(col)

删除主键:

Alter table tabname drop primary key(col)

7、创建索引:

create [unique] index idxname on tabname(col….)

删除索引:


drop index idxname

注:索引是不可更改的,想更改必须删除重新建。

8、创建视图:


create view viewname as select statement

删除视图:


drop view viewname

9、几个简单的sql语句


--选择:
select * from table1 where 范围
--插入:
insert into table1(field1,field2) values(value1,value2)
--删除:
delete from table1 where 范围
--更新:
update table1 set field1=value1 where 范围
--查找:
select * from table1 where field1 like ’%value1%’

--排序:
select * from table1 order by field1,field2 [desc]
--总数:
select count as totalcount from table1
--求和:
select sum(field1) as sumvalue from table1
--平均:
select avg(field1) as avgvalue from table1
--最大:
select max(field1) as maxvalue from table1
--最小:
select min(field1) as minvalue from table1

10、几个高级查询运算词

A:UNION 运算符
UNION 运算符通过组合其他两个结果表,并消去表中任何重复行而派生出一个结果表。当 ALL 随 UNION 一起使用时(即 UNION ALL),不消除重复行。两种情况下,派生表的每一行不是来自 TABLE1 就是来自 TABLE2。

B:EXCEPT 运算符
EXCEPT运算符通过包括所有在 TABLE1 中但不在 TABLE2 中的行并消除所有重复行而派生出一个结果表。当 ALL 随 EXCEPT 一起使用时 (EXCEPT ALL),不消除重复行。

C:INTERSECT 运算符

INTERSECT运算符通过只包括 TABLE1 和 TABLE2 中都有的行并消除所有重复行而派生出一个结果表。当 ALL随 INTERSECT 一起使用时 (INTERSECT ALL),不消除重复行。
注:使用运算词的几个查询结果行必须是一致的。


11、使用外连接

A、left (outer) join:
左外连接(左连接):结果集几包括连接表的匹配行,也包括左连接表的所有行。

select 
a.a,
a.b,
a.c,
b.c,
b.d,
b.f
from a
LEFT OUT JOIN 
b ON a.a = b.c

B:right (outer) join

右外连接(右连接):结果集既包括连接表的匹配连接行,也包括右连接表的所有行。

C:full/cross (outer) join:
全外连接:不仅包括符号连接表的匹配行,还包括两个连接表中的所有记录。

12、Group by

对列进行分组,常与聚合函数(count,sum,max,min,avg )一起使用

注意:

在分组时:不能以text,ntext,image类型的字段作为分组依据

在select统计函数中的字段,不能和普通的字段放在一起;

二、进阶部分

1、复制表(只复制表结构,源表名:a 新表名:b)

--方法一 仅用于SQL Server:
select * into b from a where 1<>1
--方法二:
select top 0 * into b from a

2、拷贝表(拷贝数据,源表名:a 目标表名:b)

insert into b(a, b, c)
select d,e,f from b;

3、子查询(表名1:a 表名2:b)

select a,b,c from a where a IN (select d from b )
或者:
select a,b,c from a where a IN (1,2,3)

4、显示文章、提交人和最后回复时间


select 
a.title,
a.username,
b.adddate
from table a,
(select max(adddate) adddate
from table 
where table.title=a.title) b

5、外连接查询(表名1:a 表名2:b)


select 
a.a,
a.b,
a.c,
b.c,
b.d,
b.f
from a
LEFT OUT JOIN b ON a.a = b.c

6、在线视图查询(表名1:a )

select * from (
SELECT a,b,c FROM a
) T
where t.a > 1;

7、between的用法,between限制查询数据范围时包括了边界值,not

between不包括
select * from table1
where time between time1 and time2

select a,b,c, from table1
where a not between 数值1 and 数值2

8、in 的使用方法

select * from table1
where a [not] in (‘值1’,’值2’,’值4’,’值6’)

9、两张关联表,删除主表中已经在副表中没有的信息

delete from table1
where not exists (
select * from table2
where table1.field1=table2.field1
)

10、四表联查问题:

select * from a
left inner join b on a.a=b.b
right inner join c on a.a=c.c
inner join d on a.a=d.d
where ...
..

11、日程安排提前五分钟提醒


select * from 日程安排
where datediff('minute',f开始时间,getdate())>5

12、一条sql 语句搞定数据库分页


select top 10 b.*
from (
select top 20 主键字段,排序字段
from 表名 order by 排序字段 desc
) a,
表名 b
where b.主键字段 = a.主键字段
order by a.排序字段具体

实现:关于数据库分页:

declare @start int,@end int
@sql nvarchar(600)
set @sql=’select top’+str(@end-@start+1)+’+from T
where rid not in(
select top’+str(@str-1)+’Rid from T where Rid>-1)’
exec sp_executesql @sql

13、前10条记录


select top 10 *
form table1
where 范围

14、包括所有在 TableA中但不在 TableB和TableC中的行并消除所有重复行而派生出一个结果表


(select a from tableA )
except 
(select a from tableB)
except 
(select a from tableC)

15、随机取出10条数据

select top 10 *
from tablename
order by newid()

16、说明:删除重复记录


--方法一
delete from tablename where id not in (select max(id) from tablename group by col1,col2,...)
--方法二
select distinct * into temp from tablename
delete from tablename
insert into tablename select * from temp

评价:这种操作牵连大量的数据的移动,这种做法不适合大容量但数据操作3),例如:在一个外部表中导入数据,由于某些原因第一次只导入了一部分,但很难判断具体位置,这样只有在下一次全部导入,这样也就产生好多重复的字段,怎样删除重复字段


alter table tablename
--添加一个自增列
add  column_b int identity(1,1)
delete from tablename
where column_b not in(
select max(column_b)
from tablename
group by column1,column2,...
)
alter table tablename drop column column_b

17、列出数据库里所有的表名

use master
go
select name from sysobjects
where type='U' // U代表用户

18、列出表里的所有的列名


use master
go
select name 
from syscolumns
where id=object_id('TableName')

19、初始化表table1


TRUNCATE TABLE table1

20、选择从10到15的记录


select top 5 *
from (
select top 15 *
from table 
order by id asc
) table_别名
order by id desc

三、开发技巧

1、where 1=1是表示选择全部,where 1=2全部不选


if @strWhere !='' 
begin
set @strSQL = 'select count(*) as Total from [' 
+ @tblName + '] where ' + @strWhere
end
else 
begin
set @strSQL = 'select count(*) as Total from [' + @tblName + ']' 
end

我们可以直接写成


set @strSQL = 'select count(*) as Total from [' 
+ @tblName + '] where 1=1 '+ @strWhere

2、收缩数据库

--重建索引
DBCC REINDEX
DBCC INDEXDEFRAG
--收缩数据和日志
DBCC SHRINKDB
DBCC SHRINKFILE

3、压缩数据库


dbcc shrinkdatabase(dbname)

4、转移数据库给新用户以已存在用户权限

exec sp_change_users_login 'update_one','newname','oldname'
go

5、检查备份集


RESTORE VERIFYONLY from disk='E:\dvbbs.bak'

6、修复数据库

ALTER DATABASE [dvbbs] SET SINGLE_USER
GO
DBCC CHECKDB('dvbbs',repair_allow_data_loss) WITH TABLOCK
GO
ALTER DATABASE [dvbbs] SET MULTI_USER
GO

7、日志清除

SET NOCOUNT ON
DECLARE @LogicalFileName sysname,
@MaxMinutes INT,
@NewSize INT

USE tablename -- 要操作的数据库名
SELECT  @LogicalFileName = 'tablename_log', -- 日志文件名
@MaxMinutes = 10, -- Limit on time allowed to wrap log.
@NewSize = 1  -- 你想设定的日志文件的大小(M)

Setup / initialize
DECLARE @OriginalSize int
SELECT @OriginalSize = size 
FROM sysfiles
WHERE name = @LogicalFileName
SELECT 'Original Size of ' + db_name() + ' LOG is ' +
 CONVERT(VARCHAR(30),@OriginalSize) + ' 8K pages or ' +
 CONVERT(VARCHAR(30),(@OriginalSize*8/1024)) + 'MB'
 FROM sysfiles
 WHERE name = @LogicalFileName
CREATE TABLE DummyTrans
(DummyColumn char (8000) not null)

DECLARE @Counter INT,
@StartTime DATETIME,
@TruncLog VARCHAR(255)
SELECT @StartTime = GETDATE(),
@TruncLog = 'BACKUP LOG ' + db_name() + ' WITH TRUNCATE_ONLY'

DBCC SHRINKFILE (@LogicalFileName, @NewSize)
EXEC (@TruncLog)
-- Wrap the log if necessary.
WHILE @MaxMinutes > DATEDIFF (mi, @StartTime, GETDATE()) -- time has not expired
 AND @OriginalSize = (SELECT size FROM sysfiles WHERE name = @LogicalFileName)
 AND (@OriginalSize * 8 /1024) > @NewSize
 BEGIN -- Outer loop.
SELECT @Counter = 0
 WHILE   ((@Counter < @OriginalSize / 16) AND (@Counter < 50000))
 BEGIN -- update
 INSERT DummyTrans VALUES ('Fill Log') DELETE DummyTrans
 SELECT @Counter = @Counter + 1
 END
 EXEC (@TruncLog)
 END
SELECT 'Final Size of ' + db_name() + ' LOG is ' +
 CONVERT(VARCHAR(30),size) + ' 8K pages or ' +
 CONVERT(VARCHAR(30),(size*8/1024)) + 'MB'
 FROM sysfiles
 WHERE name = @LogicalFileName
DROP TABLE DummyTrans
SET NOCOUNT OFF

8、更改某个表

exec sp_changeobjectowner 'tablename','dbo'

9、存储更改全部表

CREATE PROCEDURE dbo.User_ChangeObjectOwnerBatch
@OldOwner as NVARCHAR(128),
@NewOwner as NVARCHAR(128)
AS

DECLARE @Name    as NVARCHAR(128)
DECLARE @Owner as NVARCHAR(128)
DECLARE @OwnerName as NVARCHAR(128)

DECLARE curObject CURSOR FOR 
select 'Name'    = name,
   'Owner'    = user_name(uid)
from sysobjects
where user_name(uid)=@OldOwner
order by name

OPEN   curObject
FETCH NEXT FROM curObject INTO @Name, @Owner
WHILE(@@FETCH_STATUS=0)
BEGIN     
if @Owner=@OldOwner
begin
   set @OwnerName = @OldOwner + '.' + rtrim(@Name)
   exec sp_changeobjectowner @OwnerName, @NewOwner
end
-- select @name,@NewOwner,@OldOwner

FETCH NEXT FROM curObject INTO @Name, @Owner
END

close curObject
deallocate curObject
GO

10、SQL SERVER中直接循环写入数据

declare @i int
set @i=1
while @i<30
begin
    insert into test (userid) values(@i)
    set @i=@i+1
end

案例:有如下表,要求就裱中所有沒有及格的成績,在每次增長0.1的基礎上,使他們剛好及格:

Name score

Zhangshan 80

Lishi 59

Wangwu 50

Songquan 69


while((select min(score) from tb_table)<60)
begin
update tb_table set score =score*1.01
where score<60
if  (select min(score) from tb_table)>60
  break
 else
    continue
end
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