Only these four instructions are required to operate SQL data

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First of all, you should learn to install MSSQL database , There are corresponding tutorials on the Internet , It's very detailed .
Once again, learn how to build databases and tables .
MSSQL Provides a Microsoft SQLServer Management studio, Just create a database and a table here .

Here is a place to pay attention to ,n Type at the beginning ,VFP At present, it is not recommended to use . such as nvarchar(50)

I gave directions here , Baidu to find the answer , If you find , Still can't find , You can contact cat cat to help you find .

The most important thing in software development is to solve problems , The above is to solve two problems , Database system installation , Database building, database building and table building .

After the table is built , Let's learn how to manipulate data ,

At the end is SQL How to learn instructions ？
stay SQL The string in the statement is in single quotation marks 、 Single equal sign . select *、SeLeCT *： SQL Statements are case insensitive .
VFP Supported by SQL You can use double quotation marks , But in MYSQL ,MSSQL It's not allowed inside .

open Microsoft SQLServer Management studio

After inputting the instructions , You can click execute to see the result .

preparation

You can also create a table by entering the following commands in the query interface , You can also use the designer to create .

create table Student
(-------------- Create a student information table 
sId int identity(1,1) primary key,----------------- auto number 
sName nvarchar(50) not null,
sAge int not null,
sNo numeric(18,0),----------------------- ID number , Eighteen digits , The decimal is 
sSex char(2) not null,
sEmail varchar(50)
)

## Insert data into insert
Insert a row into the table （ Each column of this row has data ）
insert into surface ( Name , Name ) values( value 1, value 2)
insert student (sName,sAge,sNo,sSex,sEmail) values(‘ Zhang San ’,20,1,‘ male ’,‘[email protected]’)
insert student (sName,sAge,sNo,sSex,sEmail) values(‘ Wang Wu ’,18,1,‘ male ’,‘[email protected]’)
insert student (sName,sAge,sNo,sSex,sEmail) values(‘ Li Si ’,18,1,‘ male ’,‘[email protected]’)

## Data query

1. Query all columns
   select * from student
2. Query specified column
   select sName,sAge from student
3. Specified condition query , Search for names ＝ Zhang San's line
   select * from student where sName=‘ Zhang San ’
4. Count , Query the number of records
   select count(*) from student
5. Sum up , Query the sum of all ages
   select sum(sAge) from student

## Data update update( Data modification )

1. Update a column ：update Student set sSex = ‘ male ’
2. Update multiple columns ： update Student set sSex =‘ Woman ’,sAge = 18
3. Update some data ： update Student set sClassId= 4 where sClassId = 1, use where Statement means that only Name yes ’tom’ The line of , Be careful SQL Medium equals to judge with a single =, instead of ==.
   Where Complex logical judgments can also be used in update Student set sAge=30 where sName=‘ Hua Tuo ’ or sAge<25 ,or Or
4. The age of all students plus 1update Student set sAge = sAge + 1
   update Student set sClassId=6
   where (sAge>20 and sAge<30) or(sAge=50)
   Where Other logical operators that can be used in ：(||)or、(&&)and、(!)not、<、>、>=、<=、 <>（ or !=） etc.

priority ：

not and or, You can change the priority with parentheses .

Data deletion

Delete all data in the table ：DELETE FROM Student.
Delete Delete data , The watch is still there .
Delete You can also bring where Clause to delete part of the data ：DELETE FROM Student WHERE sAge > 20

We are currently learning to test in management tools , How to use it in the Qiyou three-tier development framework ？ see MSSQLHelper With your help .

Look at a lot of content , It is seldom done , Copy the code for an hour every day , You can learn .

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