SQL statement Summary

I. Basics

1. Description: Create a database
Create Database database-name
2. Description: delete a database.
Drop database dbname
3. Description: Back up SQL Server
--- Create a device for the backup data
Use master
Exec sp_addumpdevice 'disk', 'testback', 'c: \ mssql7backup \ mynwind_1.dat'
--- Start backup
Backup database pubs to testback
4. Description: 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:
A: Create Table tab_new like tab_old (use the old table to create a new table)
B: Create Table tab_new as select col1, col2... From tab_old definition only
5. Description: delete a new table.
Drop table tabname
6. Description: Add a column.
Alter table tabname add column Col type
Note: Columns cannot be deleted after they are added. After columns are added to DB2, the data type cannot be changed. The only change is to increase the length of the varchar type.
7. Description: Add a primary key: alter table tabname add primary key (COL)
Delete a primary key: alter table tabname drop primary key (COL)
8. Description: Create an index: Create [unique] index idxname on tabname (COL ....)
Delete index: drop index idxname
Note: The index cannot be changed. To change the index, you must delete it and recreate it.
9. Description: Create view viewname as select statement
Delete view: Drop view viewname
10. Description: several simple basic SQL statements
Select: Select * From Table1 where range
Insert: insert into Table1 (field1, field2) values (value1, value2)
Delete: delete from Table1 where range
Update: Update Table1 set field1 = value1 where range
Search: Select * From Table1 where field1 like '% value1 %' --- the like syntax is very subtle, query information!
Sort: Select * From Table1 order by field1, field2 [DESC]
Total: Select count as totalcount from Table1
Sum: Select sum (field1) as sumvalue from Table1
Average: Select AVG (field1) as avgvalue from Table1
MAX: Select max (field1) as maxvalue from Table1
Min: select Min (field1) as minvalue from Table1
11. Description: several advanced query Operators
A: Union operator
The Union operator combines two other result tables (such as Table1 and table2) and removes any duplicate rows from the table to generate a result table. When all is used together with Union (that is, Union all), duplicate rows are not eliminated. In either case, each row of the derived table is from either Table1 or table2.
B: Random t operator
The distinct t operator derives a result table by including all rows in Table 1 but not in table 2 and eliminating all repeated rows. When all is used with distinct T (distinct t all), duplicate rows are not eliminated.
C: intersect Operator
The Intersect operator derives a result table by only including the rows in Table1 and Table2 and eliminating all repeated rows. When all is used with intersect (intersect all), duplicate rows are not eliminated.
Note: The query results of several computation words must be consistent.
12. Note: use external connections
A. left Outer Join:
Left Outer Join (left join): the result set contains the matched rows in the connected table, and all rows in the left connected table.
SQL: 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 matched join rows in the connection table and all rows in the right join table.
C: Full outer join:
Full outer join: includes not only matching rows in the symbolic join table, but also all records in the two join tables.

Ii. Improvement

1. Description: copy a table (only copy structure, source table name: a new table name: B) (access available)
Method 1: Select * into B from a where 1 <> 1
Method 2: Select top 0 * into B from

2. Description: copy a table (copy data, source table name: A target table name: B) (access available)
Insert into B (a, B, c) Select D, E, F from B;

3. Description: Table Copying across databases (absolute path for specific data) (access is available)
Insert into B (a, B, c) Select D, E, F from B in 'specific database' where Condition
Example:... from B in '"& server. mappath (". ") &" \ data. mdb "&" 'where ..

4. Description: subquery (table name 1: Table A name 2: B)
Select a, B, c from a where a in (select D from B) or: select a, B, c from a where a in (1, 2, 3)

5. Description: displays the article, Submitter, and 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

6. Description: External join query (table name 1: Table A 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

7. Description: Online View query (table name 1:)
Select * from (select a, B, c from a) t where T. A> 1;

8. Description: between usage. When between restricts the Data Query range, it includes the boundary value. Not between does not include
Select * From Table1 where time between time1 and time2
Select a, B, c, from Table1 where a not between value 1 and value 2

9. Description: How to Use in
Select * From Table1 where a [not] In ('value 1', 'value 2', 'value 4', 'value 6 ')

10. Description: two associated tables are used to delete information that is not in the secondary table.
Delete from Table1 where not exists (select * From Table2 where table1.field1 = table2.field1)

11. Notes: four table join query problems:
Select * from a left inner join B on. A = B. B right inner join C on. A = C. C inner join D on. A = D. d Where .....

12. Note: Five minutes ahead of schedule reminder
SQL: Select * from Schedule where datediff ('minute ', F Start Time, getdate ()> 5

13. Note: One SQL statement is used to handle database paging.
Select top 10 B. * From (select top 20 primary key field, sorting field from table name order by sorting field DESC) A, table name B where B. primary key field =. primary key field order by. sorting Field

14. Note: The first 10 records
Select top 10 * Form Table1 where range

15. Note: select all the information of the largest record of a corresponding to the data with the same B value in each group (similar usage can be used for the monthly ranking of the forum and Analysis of popular products each month, rank by subject score, etc .)
Select a, B, c from tablename Ta where a = (select max (a) from tablename TB where TB. B = TA. B)

16. Description: includes all rows in tablea but not in tableb and tablec and removes all repeated rows to derive a result table.
(Select a from tablea) Before t (select a from tableb) Before t (select a from tablec)

17. Description: 10 data records are randomly taken out.
Select top 10 * From tablename order by newid ()

18. Description: randomly selected records
Select newid ()

19. Note: delete duplicate records
Delete from tablename where id not in (select max (ID) from tablename group by col1, col2 ,...)

20. Description: Lists All table names in the database.
Select name from sysobjects where type = 'U'

21. Note: List all
Select name from syscolumns where id = object_id ('tablename ')

22. Description: lists the fields of type, vender, and PCs, which are arranged by the Type field. case can be easily selected, similar to case in select.
Select Type, sum (Case vender when 'a then PCs else 0 end), sum (Case vender when 'C' then PCs else 0 end ), sum (Case vender when 'B' then PCs else 0 end) from tablename group by type
Display result:
Type vender PCs
Computer A 1
Computer A 1
Cd B 2
Cd a 2
Mobile phone B 3
Mobile phone C 3

23. Description: Initialize table 1.

Truncate table Table1

24. Description: select a record from 10 to 15.
Select top 5 * from (select top 15 * from Table order by id asc) Table _ alias order by ID DESC

Iii. Skills

1. 1 = 2. It is used in combination of SQL statements.

"Where 1 = 1" indicates that all "where 1 = 2" are not selected,
For example:
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 Anding '+ @ strwhere

2. shrink the database
-- Re-Indexing
DBCC reindex
DBCC indexdefrag
-- Shrink data and logs
DBCC shrinkdb
DBCC shrinkfile

3. compress the database
DBCC shrinkdatabase (dbname)

4. Transfer the database to a new user with the existing user permission
Exec sp_change_users_login 'Update _ one', 'newname', 'oldname'
Go

5. Check the backup set
Restore verifyonly from disk = 'e: \ dvbbs. Bak'

6. Restore 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 clearing
Set nocount on
Declare @ logicalfilename sysname,
@ Maxminutes int,
@ Newsize int

Use tablename -- Name of the database to be operated
Select @ logicalfilename = 'tablename _ log', -- Log File Name
@ Maxminutes = 10, -- limit on time allowed to wrap log.
@ Newsize = 1 -- the size of the log file you want to set (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) + '8 K 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) + '8 K pages or '+
Convert (varchar (30), (size * 8/1024) + 'mb'
From sysfiles
Where name = @ logicalfilename
Drop table dummytrans
Set nocount off

8. Description: modify 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
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. Data is written cyclically in SQL Server.
Declare @ I int
Set @ I = 1
While @ I <30
Begin
Insert into test (userid) values (@ I)
Set @ I = @ I + 1
End

 

Iv. SQL Server nested SELECT statement

Nested select statements are also called subqueries, for example:

Select name from BBC where region = (select region from BBC where name = 'Brazil ')

 

The query result of one SELECT statement can be used as the input value of another statement.

The preceding SQL statement is used to obtain all countries in the same region as 'Brazil '(Brazil.

Subqueries can appear not only in the WHERE clause, but also in the from clause. They can be used as a temporary table or in the select list and returned as a field value. This section describes only subqueries in the where clause.

When subqueries are used in the WHERE clause, an error that is easy to make in actual use is described here.

Generally, as in the preceding example, nested statements are always compared with a value.

Statement (select region from BBC where name = 'Brazil ') should return only one region, that is, 'americas '. However, if we insert another record with the Region Europe and country name Brazil in the table, what will happen?

This will cause a statement running error. Because the syntax of this SQL statement is correct, the database engine starts to execute the statement, but an error occurs when it is executed to an external statement.

The external statement is like select name from BBC where region = ('americas', 'Europe'). Of course, an error is returned.

Is there a way to solve this problem, of course. Some SQL query conditions allow you to operate on the list values (that is, multiple values.

For example, the "in" operator can test whether a value is in a list.

The following statement can be executed securely without errors, no matter how many records in the table contain the cmdils

Reference content is as follows:

 

Select name from BBC where region in
(Select region from BBC where name = 'Brazil ')

 

Let's take a look at some specific instances.

1. Name of a country with more population than Russia (Russia)

Reference content is as follows:

 

Select name from BBC
Where population>
(Select population from BBC
Where name = 'Russia ')

 

2. provide all information about all countries in the region where 'India "and 'ira' (Iran) are located.

Reference content is as follows:

 

Select * from BBC
Where region in
(Select region from BBC
Where name in ('India ', 'irance '))

 

3. European countries with GDP per capita exceeding 'United Kingdom '(UK) are provided.

Reference content is as follows:

 

Select name from BBC
Where region = 'Europe' and GDP/population>
(Select GDP/population from BBC
Where name = 'United Kingdom ')