MySQL add, delete, modify, query & advanced query statements

Catalog

One 、 Preface

Two 、 Basic query

3、 ... and 、 Filter query

Four 、 Fuzzy query

5、 ... and 、 Sort query

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One 、 Preface

We read the last article together MySQL Account management , There are also basic operations such as database and table creation , Let's take a look at this article MySQL Some of the basics CRUD Statements and some more advanced queries , We use this employee form for the whole process ：t_mysql_employees

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Two 、 Basic query

1.1  increase

--  increase 
insert into t_mysql_employees 
values(207,'Xiao','Leaf','CHAO','520.1234.1217','AD_PRES',100000,0.9,null,110,'2003-12-17')

--  Query test

select * from t_mysql_employees where last_name = 'Leaf'; 

  Query results ：

1.2  modify

--  modify 
update t_mysql_employees set employee_id = 001 where last_name = 'Leaf';

--  Query test

select * from t_mysql_employees where last_name = 'Leaf'; 

  Query results ：

1.3  Delete

--  Delete 
delete from t_mysql_employees where last_name = 'Leaf';

 --  Query test

select * from t_mysql_employees where last_name = 'Leaf'; 

Query results ：

1.4  Basic query

	#1. A single field in a query table 
	select job_id from t_mysql_employees;
	#2. Multiple fields in the query table 
	select job_id,email from t_mysql_employees;
	#3. Query all fields in the table 
	select * from t_mysql_employees;
	#4. Query constant value 
	SELECT 100;
	SELECT 'john';
	#5. Query expression 
	SELECT 100%98;
	#6. Query function 
	SELECT VERSION();

Here, these basic queries don't put too many screenshots of query results ~

1.5  Take the alias

	#7. names 
	select email  Mailbox number  from t_mysql_employees;

result ：

  

1.6  duplicate removal

	#8. duplicate removal ：distinct
	​# Case study ： Query all department numbers involved in the employee table 
	select DISTINCT job_id from t_mysql_employees

result ：

Be careful ：

    MySQL in ：+ The role of No
    java Medium + Number ：
    ① Operator , Both operands are numeric
    ② Connector , As long as one of the operands is a string
    ​mysql Medium + Number ：
     Just one function ： Operator  

1.7  Query the current time

	--  Query the current time 
	select now();

  Query results ：

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3、 ... and 、 Filter query

3.1  One 、 Filter by conditional expression

# Case study 1： Query salary >12000 Employee information

select * from t_mysql_employees where salary > 1200;

Query results ：

# Case study 2： Query department number is not equal to 90 The employee name and department number of the

Two ways of writing ：

--  How to write it 1​
select last_name,department_id from t_mysql_employees
where department_id <> 90;
--  How to write it 2
​select last_name,department_id from t_mysql_employees
where not(department_id = 90);

  Query results ：

3.2 Filter by logical expression

# Case study 1： Check salary at 10000 To 20000 Between the employee's name 、 Salary and bonus

select last_name,salary,commission_pct from t_mysql_employees 
where salary between 10000 and 20000;

Query results ：

# Case study 2： The inquiry department number is not in 90 To 110 Between , Or pay more than 15000 Employee information

select * from t_mysql_employees 
where not(department_id between 90 and 110) or salary > 1500;

  Query results ：

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Four 、 Fuzzy query

4.1 like

# Case study 1： Query employee name contains characters a Employee information

select * from t_mysql_employees where last_name like '%a%'

# Case study 2： The third character in the query employee name is e, The fifth character is a The name and salary of the employee

select last_name,salary from t_mysql_employees where last_name like '_e_a%'

# Case study 3： The second character in the employee name is _ Employee name of

notes ：ESCAPE It's an escape , Give Way $ Take a place .

select last_name from t_mysql_employees where last_name like '_$_%' ESCAPE '$'

Query results ：

4.2 between and

# Case study 1： Query the employee number in 100 To 120 Employee information between

select * from t_mysql_employees where employee_id between 100 and 120; 

Query results ：

 4.3 in

# Case study ： The job number of the employee is IT_PROG、AD_VP、AD_PRES An employee's name and job number in the

select last_name,job_id from t_mysql_employees 
where job_id in ('IT_PROG','AD_VP','AD_PRES');

Query results ：

  

4.4  is null && is not null

# Case study 1： Query the employee name and bonus rate without bonus

select last_name,commission_pct from t_mysql_employees where commission_pct is null;

Query results ：

    
# Case study 2： Check the name and bonus rate of employees with bonus

select last_name,commission_pct from t_mysql_employees 
where commission_pct is not null;

Query results ：

4.5  Safety is equal to

# Case study 1： Query the employee name and bonus rate without bonus

select first_name,commission_pct from t_mysql_employees 
where  commission_pct <=> null

Query results ：

    # Case study 2： Query salary as 12000 Employee information

​select * from t_mysql_employees where  salary <=> 12000;

Query results ：

Let's compare is null  and   Safety is equal to <=>  Characteristics ：

IS NULL： Can only judge NULL value , High readability , It is recommended to use
<=>： You can judge NULL value , You can also judge ordinary values , Less readable

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5、 ... and 、 Sort query

5.1 order by Clause

​5.1.1、 Sort by a single field
    # Case study ： Sort by employee table salary

select last_name,salary from t_mysql_employees order by salary desc

    #2、 Add filter criteria and sort
    ​# Case study ： Check department number >=90 Employee information , And in descending order of employee number

select * from t_mysql_employees where department_id >= 90 order by employee_id desc

    #3、 Sort by expression
    # Case study ： Query employee information In descending order of annual salary

select em.salary*12*(1+ifnull(commission_pct,0)),em.* from t_mysql_employees em 
order by salary*12*(1+ifnull(commission_pct,0)) desc

Query results ：

    ​​
    #4、 Sort by alias
    # Case study ： Query employee information In ascending order of annual salary  

select * from t_mysql_employees order by salary*12*(1+ifnull(commission_pct,0));

    #5、 Sort by function
    # Case study ： Query employee name , And in descending order of the length of the names     

select last_name,CONCAT(first_name,last_name),length(CONCAT(first_name,last_name)) 
from t_mysql_employees order by length(CONCAT(first_name,last_name)) desc;

Query results ：

    ​​
    #6、 Sort by multiple fields
    ​# Case study ： Query employee information , It is required that the salary be in descending order first , Press again employee_id Ascending

select * from t_mysql_employees order by salary desc,employee_id asc;

  Query results ：

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OK, These are Leaf Bring about MySQL Related sentences of , Basic query , You can pay attention to the progress together if you like ！ I'll see you next time ！！！