PostgreSQL：使用变量时出现语法错误

Question

I am trying to find cumulative sum of a column. Know that, window function can achieve this, however I want to achieve this using variables. This is my code.

DECLARE csum INTEGER := 0;
SELECT 
    employee_id,
    department_id,
    boss_id,
    name,
    salary,
    (csum := csum + salary) AS cum_salary
FROM employees

I get the below error message. How do i fix this?

org.postgresql.util.PSQLException: ERROR: syntax error at or near "INTEGER"
  Position: 14
DECLARE csum INTEGER := 0;
             ^
SELECT 

---

EDIT: I was trying to achieve something similar I have done in MySQL. However, realised that PostgreSQL doesn't support this. Thanks.

Answer 1

No need for a hack with variables (which don't exist in standard SQL or Postgres to begin with).

This can easily be done using a window function. However a cumulative sum only makes sense if you also provide a sort order for the rows.

SELECT 
    employee_id,
    department_id,
    boss_id,
    name,
    salary,
    sum(salary) over (order by ????)
FROM employees