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SQL column

Summary of basic knowledge of SQL database

Summary of advanced knowledge of SQL database

1. Basic part

1. Create a database

CREATE DATABASE dbname

2. Delete the database

DROP DATABASE dbname

3. Create a new table

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

Create a new table based on an existing table:

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

4. Delete the new table

DROP TABLE tablename

5. Add a column

Alter table tabname add column col type

6. Add the primary key:

Alter table tabname add primary key(col)

Delete the primary key:

Alter table tabname drop primary key(col)

7. Create an index:

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

Delete index:

drop index idxname

Note: The index cannot be changed, you must delete it and rebuild it if you want to change it.

8. Create a view:

create view viewname as select statement

Delete view:

drop view viewname

9, a few simple SQL statements

--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. Several advanced query operators

A: UNION operator The
UNION operator derives a result table by combining the other two result tables and eliminating any duplicate rows in the table. When ALL is used with UNION (that is, UNION ALL), duplicate rows are not eliminated. In both cases, each row of the derived table is either from TABLE1 or from TABLE2.

B: EXCEPT operator The
EXCEPT operator derives a result table by including all rows in TABLE1 but not in TABLE2 and eliminating all duplicate rows. When ALL is used with EXCEPT (EXCEPT ALL), duplicate rows are not eliminated.

C: INTERSECT operator

The INTERSECT operator derives a result table by including only the rows in both TABLE1 and TABLE2 and eliminating all duplicate rows. When ALL is used with INTERSECT (INTERSECT ALL), duplicate rows are not eliminated.
Note: Several query result rows using operands must be consistent.

11. Use outer join
A, left (outer) join:
Left outer join (left join): The result set includes the matching rows of the join table, as well as all the rows of the left join table.

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

Right outer join (right join): The result set includes both matching join rows of the join table and all rows of the right join table.

C: full/cross (outer) join:
Full outer join: not only includes the matching rows of the symbolic link table, but also includes all the records in the two joined tables.

12、Group by

Group the columns, often used with aggregate functions (count, sum, max, min, avg)

note:

When grouping: text, ntext, image type fields cannot be used as the grouping basis

The fields in the select statistical function cannot be put together with ordinary fields;

2. Advanced part

1. Copy table (only copy table structure, source table name: a new table name: 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. Copy table (copy data, source table name: a target table name: b)

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

3. Subquery (table name 1: a table name 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. Display the article, the submitter and the last reply time

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

5. Outer join query (table name 1: a table name 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. Online view query (table name 1: a)

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

7. The usage of between, the boundary value is included when the range of the query data is restricted by between, 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. How to use in

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

9. Two related tables, delete the information in the main table that is not in the secondary table

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

10. Questions about the four-meter joint inspection:

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. Remind five minutes in advance of the schedule

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

12. One sql statement to do database paging

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

Implementation: About database paging:

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. The first 10 records

select top 10 *
form table1
where 范围

14. Include all rows in TableA but not in TableB and TableC and eliminate all duplicate rows to derive a result table

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

15. Randomly fetch 10 pieces of data

select top 10 *
from tablename
order by newid()

16. Description: Delete duplicate records

--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

Evaluation: This operation involves the movement of a large amount of data. This approach is not suitable for large-capacity but data operation 3), for example: importing data in an external table, due to some reasons only import part of the first time, but it is difficult Determine the specific location, so that it will only be imported in the next time, so that a lot of duplicate fields will be generated, how to delete duplicate fields

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. List all table names in the database

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

18. List all the column names in the table

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

19. Initialize table table1

TRUNCATE TABLE table1

20. Select records from 10 to 15

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

Three, development skills

1. Where 1=1 means to select all, where 1=2 does not select all

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

We can directly write

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

2. Shrink the database

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

3. Compress the database

dbcc shrinkdatabase(dbname)

4. Transfer the database to the new user with existing user rights

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

5. Check the backup set

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

6. Repair the database

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. Log clear

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. Change a table

exec sp_changeobjectowner 'tablename','dbo'

9. Store and change all tables

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. Write data directly in SQL SERVER circularly

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

Case: There is the following table, all the failing grades in the request will be mounted on the basis of an increase of 0.1 each time, so that they just pass:

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