string_agg() in postgres

CREATE TABLE employee(
    id SERIAL not NULL PRIMARY KEY ,
    CompanyName VARCHAR,
    EmployeeName VARCHAR,
    Salary NUMERIC
);

INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Sony','Bob',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Sony','Jhon',2000);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Sony','Dow',15000);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Sony','Alice',5602);

INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Google','Jade',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Google','Penny',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Google','Kat',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Google','Merly',1500.55);

INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Hitachi','Raymond',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Hitachi','Skye',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Hitachi','Sova',1500.55);
INSERT INTO employee(CompanyName,EmployeeName,Salary) VALUES('Hitachi','Jenny',1500.55);

SELECT companyname As CompanyName, STRING_AGG(employeename,', ') as Employees
FROM employee
GROUP BY companyname;


SELECT companyname As CompanyName, STRING_AGG(employeename,', ') as Employees
FROM employee
GROUP BY companyname;


SELECT companyname As CompanyName, STRING_AGG(employeename,', ') as Employees
FROM employee
GROUP BY companyname;

SELECT companyname As CompanyName, STRING_AGG(DISTINCT employeename,', ' ORDER BY employeename desc) as Employees
FROM employee
GROUP BY companyname;