How to update table on postgres with join statement - postgresql

Question

I have three tables on postgresql DB, and tried to update table but I failed to get result what I want. Please help me with getting valid result.
The first table is "employee".
On this table, the first three characters of "employee_id" mean employee type.
For example, employee_id="AA1-11111" is a member of employee_type="AA1".
employee_id
department
AA1-11111
A
AA1-22222
B
AB1-11111
A
The second table is "assessment".
On this table, assessment criteria is defined for (employee_type, department).
For example, an employee of employee_type="AA1" and department="A" will be evaluated by assessment_criteria="XX1X".
employee_type
department
assessment_criteria
AA1
A
XX1X
AA1
B
XX1Y
AA2
A
XX2X
The third table is "employee_assessment". On this table assessment_criteria for each employee is defined. (This table is calculated from "employee" and "assessment" by night batch processing.)
employee_id
department
assessment_criteria
AA1-11111
A
XX1X
AA1-22222
B
XX1Y
AB1-11111
A
Null
What I want to do is... to update "employee_assessment" table when "assessment" table is updated.
When "assessment" table is updated as like below...
employee_type
department
assessment_criteria
AA1
A
XX1X
AA1
B
NEW
AA2
A
Null
I want to update "employee_assessment" table like this.
employee_id
department
assessment_criteria
AA1-11111
A
XX1X
AA1-22222
B
NEW
AB1-11111
A
Null
I tried
UPDATE
employee_assessment
SET assessment_criteria=employee_assessment.assessment_criteria
FROM employee
LEFT JOIN (SELECT employee_id, LEFT(employee_id,3) as emp_type, department as emp_department from employee) as t1
ON
employee.employee_id=t1.employee_id
and
employee.department=t1.emp_department
left join assessment
on
t1.emp_type=assessment.employee_type
and
t1.emp_department=assessment.department;
But I got this result.
employee_id
department
assessment_criteria
AA1-11111
A
XX1X
AA1-22222
B
XX1X
AB1-11111
A
XX1X
My query seems to be wrong.

Answer 1

The actual cause of the problem is that you schema isn't properly normalized. Therefore you should solve this by fixing and normalizing your schema. Then you can simply use a view, that is "updated" automatically.
First have tables for the types and departments (unless you have that already (that's unclear)).
CREATE TABLE type
(id serial,
name varchar(64),
PRIMARY KEY (id));
CREATE TABLE department
(id serial,
name varchar(64),
PRIMARY KEY (id));
Then, in the table for the employees, just reference the types and departments. Don't have a column that actually are two columns, i.e. the type id has to have its own column and must not be concatenated to any other.
CREATE TABLE employee
(id serial,
type integer,
department integer,
given_name varchar(64),
surname varchar(64),
PRIMARY KEY (id),
FOREIGN KEY (type)
REFERENCES type
(id),
FOREIGN KEY (department)
REFERENCES department
(id));
In the table for the assessments reference the types and departments too.
CREATE TABLE assessment
(id serial,
type integer,
department integer,
name varchar(64),
criteria varchar(64),
PRIMARY KEY (id),
FOREIGN KEY (type)
REFERENCES type
(id),
FOREIGN KEY (department)
REFERENCES department
(id));
Now you can create view for the employee assessments that joins the data from the other tables and is always up to date. There's no need for any manual UPDATE.
CREATE VIEW employee_assessment
AS
SELECT e.id employee_id,
e.department employee_department,
a.criteria assessment_criteria
FROM employee e
LEFT JOIN assessment a
ON a.type = e.type
AND a.department = e.department;
A view also has the advantage that it cannot contain inconsistent data as the table you have now could.