1-3 using SQL to manage databases

What is? SQL?

SQL（ English full name ：Structured Query Language） Structured query language , A programming language designed to access and process databases . Can let us in the form of programming , operation Data in the database .

Three key points ：

1. SQL Is a database programming language
2. Use SQL Language code , be called SQL sentence
3. SQL Language can only be used in relational databases （ for example MySQL、Oracle、SQL Server）. Non relational database （ for example Mongodb） I won't support it SQL Language .

SQL What can be done ?

1. Query data from database
2. Insert new data into item data
3. Update the data in the database
4. Delete data from database
5. You can create a new database
6. New tables can be created in the database
7. You can create stored procedures in the database 、 View

SQL Learning objectives of ?

Query data （select）、 insert data （insert into）、 Update data （update）、 Delete data （delete）

Extra to master 4 Kind of SQL grammar ：
where Conditions 、and and or Operator 、order by Sort 、count(*) function

SQL Of SELECT sentence

SELECT Statement to query data from a table . The result of the execution is stored in a result （ Called result set ）. The syntax is as follows :

// Query all columns 
SELECT * FROM  The name of the table 
// Query specified column 
SELECT  Column name  FROM  The name of the table 

--  adopt * hold users Query all the data in the table 
-- select * from users

--  from users In the table username and password Find out the corresponding data 
select username, password from users

INSERT INTO Statement is used to insert a new data row into a data table

--  towards users In the table , Insert new data ,username The value of is  tony stark password  The value of is  098123
-- insert into users (username,password) values ('tony stark','098123')

SQL Of UPDATE sentence

--  hold users In the table id by 4 The user password of , Updated to 888888
-- update users set password='888888' where id=4
-- select * from users
-- update users set password='admin123',status=1 where id=2
-- select *from users

SQL Of DELETE sentence

Be careful ： When deleting table data, you must add one where Conditions , Otherwise, the data of the whole table will be deleted

--  Delete users In the table id=4 The data of 
-- delete from users where id=4
select *from users