SQL statement for Java Pen questions (single table)

Title: There is a table in the system Wcemploy (employee number, name, department name, job, salary)

I. Please write out the statement of the building form

1 CREATE TABLE Wcemploy (2     int auto_increment PRIMARY KEY, 3     Char (8null,4     Char (+), 5     Char (8), 6     Double 7 )

Two. Inserting data

1 Insert  intoWcemployValues(NULL,'Zhang San','Workshop One','Fitter',6000)2 Insert  intoWcemployValues(NULL,'John Doe','Workshop One','Electrician',8000)3 Insert  intoWcemployValues(NULL,'Harry','Workshop II','Workshop Director',10000)

1 Insert  intoWcemployValues(NULL,'Tai Day Day','Workshop One','Fitter',6000),2(NULL,'Wind High set fire','Workshop One','Electrician',8000),3(NULL,'Volvo','Workshop II','Workshop Director',10000),4(NULL,'CVBS','Workshop II','Fitter', -),5(NULL,'Single person','Workshop Three','Fitter',4500),6(NULL,'Head Dog','Workshop II','Fitter',6000),7(NULL,'Harem','Workshop One','Fitter', the)

Multiple data insertions

When inserting the data, an error occurred, inserting the Chinese character data errors

Modify the database properties of the MySQL database property character set to

Three. Query statements

1. Please use an SQL statement to query the total number of people in each department

Select department_name,COUNT(DISTINCT from wcemployGROUP  by Department_name

2. Use an SQL statement to find out the average salary of the staff in different departments as "fitter"

Select department_name,AVG from wcemploywhere type= ' Fitter ' GROUP  by department_name//If there is no grouping, an error occurs

3. Please use an SQL statement to find out the department of the staff with the "fitter" average salary higher than 2000 in different departments

Select department_name,AVG(Salary) as from wcemploywhere type = ' Fitter ' GROUP  by Department_name  having AVG (Salary) >  -

Error wording:

Select department_name,AVG(Salary) as from wcemploywhere type = ' Fitter '   and AVG (Salary) >  - GROUP  by Department_name

4. Please use an SQL statement to query employee information for each department below average salary

Select *  from Wcemploy W, (SelectAVG as davg,department_name//a w table  from WcemployGROUP by department_name) t//a T-table where=  and W.salary<DAvg

1 SelectW.*, DAvg from2 Wcemploy W3  Left Join(Select AVG(Salary) asDavg,department_name4  fromWcemploy5 GROUP  byDepartment_name) T onW.department_name=T.department_name6 whereW.department_name=T.department_name andW.salary<DAvg

　　

SQL statement for Java Pen questions (single table)