Inner Join Right Approach for this Query? - mysql

Question

I would like some help with an SQL query that I am struggling with, Ive got 90% of what I need it to do done its just the last bit that I'm having a little issue with.
Database Design
I have the following database Schema
CREATE TABLE IF NOT EXISTS EMPLOYEES(
ID INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
FIRST_NAME VARCHAR(255) NOT NULL,
LAST_NAME VARCHAR(255) NOT NULL,
SEX CHAR(1) NOT NULL,
COST INTEGER NOT NULL
);
CREATE TABLE IF NOT EXISTS SKILLS(
ID INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
SKILL VARCHAR(300) NOT NULL
);
CREATE TABLE IF NOT EXISTS EMPLOYEE_SKILLS(
EMPLOYEE_ID INTEGER NOT NULL,
SKILL_ID INTEGER NOT NULL,
PROFICIENCY SET('1','2','3','4') NOT NULL,
PRIMARY KEY(EMPLOYEE_ID,SKILL_ID),
UNIQUE INDEX(SKILL_ID,EMPLOYEE_ID),
FOREIGN KEY (EMPLOYEE_ID) REFERENCES EMPLOYEES(ID) ON UPDATE CASCADE ON DELETE CASCADE,
FOREIGN KEY (SKILL_ID) REFERENCES SKILLS(ID) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS PROJECTS(
ID INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
NAME VARCHAR(300) NOT NULL,
LOCATION VARCHAR(255) DEFAULT NULL,
INCOME INTEGER NOT NULL
);
CREATE TABLE IF NOT EXISTS TASKS(
ID INTEGER AUTO_INCREMENT NOT NULL PRIMARY KEY,
NAME VARCHAR(300) NOT NULL,
PROJECT_ID INTEGER NOT NULL,
DATE_FROM DATE NOT NULL,
DATE_TO DATE NOT NULL,
COMPLETED BOOLEAN DEFAULT 0,
FOREIGN KEY (PROJECT_ID) REFERENCES PROJECTS(ID) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS TASK_SKILLS(
TASK_ID INTEGER NOT NULL,
SKILL_ID INTEGER NOT NULL,
PROFICIENCY_REQUIRED SET('1','2','3','4') NOT NULL,
PRIMARY KEY(TASK_ID,SKILL_ID),
UNIQUE INDEX(SKILL_ID,TASK_ID),
FOREIGN KEY (TASK_ID) REFERENCES TASKS(ID) ON UPDATE CASCADE ON DELETE CASCADE,
FOREIGN KEY (SKILL_ID) REFERENCES SKILLS(ID) ON UPDATE CASCADE ON DELETE CASCADE
);
CREATE TABLE IF NOT EXISTS ASSIGNED_TO(
EMPLOYEE_ID INTEGER NOT NULL,
TASK_ID INTEGER NOT NULL,
DATE_ASSIGNED DATETIME NOT NULL,
PRIMARY KEY(EMPLOYEE_ID,TASK_ID),
UNIQUE INDEX(TASK_ID,EMPLOYEE_ID),
FOREIGN KEY (EMPLOYEE_ID) REFERENCES EMPLOYEES(ID) ON UPDATE CASCADE ON DELETE CASCADE,
FOREIGN KEY (TASK_ID) REFERENCES TASKS(ID) ON UPDATE CASCADE ON DELETE CASCADE
);
Query
So the query that I would like to create would be to return every EMPLOYEE within the database along with their SKILLS and the PROFICIENCY of their skill. This was the part of the query where I had no trouble with and I have the following query:
SELECT EMPLOYEES.ID, CONCAT_WS(' ',EMPLOYEES.FIRST_NAME,EMPLOYEES.LAST_NAME) AS NAME, GROUP_CONCAT(SKILLS.SKILL),EMPLOYEES.COST,GROUP_CONCAT(EMPLOYEE_SKILLS.PROFICIENCY)
FROM EMPLOYEE_SKILLS
JOIN EMPLOYEES ON EMPLOYEE_SKILLS.EMPLOYEE_ID = EMPLOYEES.ID
JOIN SKILLS ON EMPLOYEE_SKILLS.SKILL_ID = SKILLS.ID
GROUP BY EMPLOYEES.ID
The above query gives me the majority of what I want, where it returns every employee within the database and their associated skill and the level that they know it at.
The thing that I am struggling with now is that I would also like to join up this query to also look into the ASSIGNED_TO table of the database as well, where I would like to find all the employees within the organisation (assigned to a task or not) and return the TASK ID that they have been assigned and the start and end date of said task.
Ive tried simply adding another join to the ASSIGNED_TOtable within the above query but it doesn't give me the desired output. I'm suspecting because I am grouping by the employee id. Would I need to use something like two queries to get what I want, for example and inner select and an outer select and do an inner join between them? Not really sure what the approach would be for this query.
Sorry for the long post and any help will be much appreciated.
Thanks.