Basic Connection
select clause list, each target should add the base table name before the column
It shall include all groups from clause tables used
where clause should be equal define a connection
Internal link
The more qualified data tables singled out in the Link is an equivalent connection
The SELECT the SELECT List ( lookup target column)
The INNER table1 the FROM the JOIN (represented by the connection) Table2 [the ON Join_ Conditions (equivalent connections) ]
[WHERE search_ conditions]
[ORRDER BY order_ expression]
practice:
SELECT A. class name, A. Class size, B. Name, B. Contact
Class information FROM A Inner the Join message B counselor
ON A. instructor = B. ID counselor
Where B. Sex = 'female'
inner can be canceled
Left outer join
Select A. class name, A. Class size, B. Name, B. Contact
From the LEFT instructor information B. Outer the Join A class information
ON A. instructor = B. ID counselor
Where A. class size> 20
Ourer can be canceled
Right outer join
Select A. class name, A. Class size, B. Name, B. Contact
From RIGHT class information A. Outer the Join message B counselor
ON A. instructor = B. ID counselor
Where A. class size> 20
Fully connected
Select A. class name, A. Class size, B. Name, B. Contact
From instructor information B FULL outer join class information A.
ON A. instructor = B. ID counselor
Cross-connect
Syntax
Select select_list
FROM table1 CROSS JOIN (连接）table2
[WHERE search_conditions] (screening result)
[ORDeR BY order_expression]
practice
Select A. class name, A. The number, B. Name
Information From A cross join class B information counselor
Since the connection
practice
Select A. class name, A. Class size, B. Class name
From information class A, class B information
Where a. = The number of class B. and A. Class No. Class number <> B. And A. Class No. Class name = "name query class'
Joint inquiry
Syntax
Select select_list
From table_source
[where search_conditions]
{Union [all] (combined with the two query results)
Selectselect_list
From table_source
[where search_conditions]}
[order by order_expression]
all can be canceled, it does not use the results of two queries to filter out duplicate rows
note:
When using UNION queries, connect two result sets must have the same number of expressions in their target list, and the data content as consistent as possible
practice
Select A. No. achievement, A. scores, B. Name
FROM student achievement information A. Information B
Where A. student number = B. Student ID and A. Course ID = '2' and a. Examination ID = '0808'
UNION
Select '' sum (Score) 'Total'
FROM student achievement information A. Information B
Where A. student number = B. Student ID and A. Course ID = '2' and a. Examination ID = '0808'
ORDER BY score
Using Subqueries
Select A. No. achievement, A. scores, B. Name
FROM student achievement information A. Information B
Where A. student number = B. Student ID and A. Course ID = '2' and a. Examination ID = '0808'
And a. Fraction <(
The SELECT AVG (score) FROM student achievement information A. Information B
Where A. student number = B. Student ID and A. Course ID = '2' and a. Examination ID = '0808'
)
Nested subqueries
Select A. No. achievement, A. scores, B. Name
FROM student achievement information A. Information B
Where A. student number = B. Student ID and A. Course ID = '2' and a. Examination ID = '0808'
And a. Student ID <(
Select Student ID FROM Class B Information A. Student Information
Where A. Class ID = B. Student number and B. relevant class = '2' and a. Instructor = (
Sellect counselor counselor number from information where name = 'Query Name'
）
xml query
Query Format
practice
FOR XML clause
Table database system can be retrieved by for xml clause and set out to obtain data from the automatic mode represented as XML format.
mode:
RAW mode, AUTO mode, EXPLICIT mode, PATH mode
RAW mode
Select A. class name, A. Class size, B. Name, B. Contact
From class information A. instructor information B
Where A. instructor = B. ID counselor
For cml raw
AUTO mode
Select A. class name, A. Class size, B. Name, B. Contact
From class information A. instructor information B
Where A. instructor = B. ID counselor
For cml auto
EXLSTS keyword query
Select a. * From grade information
Where exists (select * exams Bwhere b. Exam code = a. Exam code and b. Examination ID = '0809')
User Login judgment
Declare @username varchar (20)
Declare @pwd varchar(20)
Set @username = '01010202'
Set @pwd = 'ha'
If exists (select * from where student information Student ID = @ yserbane and name = @ owd)
Print 'successful landing'
Else
Print 'login failed'
INTERSECT query cross
Select from a. Achievement information a, scores b. Name achievement information from a, b student information
Where a. Student number = b. Student number and a. Course Code = 2 and a. Examination ID = '0801'
Intersect
Select a. Performance numbers, a. Fraction, A. Name from
(
Select top 10 a. Achievement information a, scores, b. From grade information a, b student information
Where a. Student number = b. Student number and a. Exam Number = '0801'order by a. Fraction desc
)a
EXCEPT poor query
Select from a. Achievement information a, scores b. Name achievement information from a, b student information
Where a. Student number = b. Student number and a. Course Code = 2 and a. Examination ID = '0801'
EXCEPT
Select a. Performance numbers, a. Fraction, A. Name from
(
Select top 10 a. Achievement information a, scores, b. From grade information a, b student information
Where a. Student number = b. Student number and a. Exam Number = '0801'order by a. Fraction desc
)a
