SQL将2个表合并为1

Question

I have put below two SQL statements that I want to join, they both work perfectly fine separately but when trying to join them I don't get the result I'm looking for. I'll explain the 3 tables I'm using and put the code below that.

There are 3 tables stoctran , stock and department . Let's start with department , it contains a department and a description (example: 01, 'Food'). Then there is the stock table which contains code, description, department(code), onhand(number of items in sotre) and avrgcost(average cost of the product). Then finally there is stoctran this table has every sale that gets made per product in it and the fields are as follows: itemcode(same as in stock), tcode (code that distinguishes between an invoice and a credit note), amount (the amount that was charged for that item), cost (the cost for that item), department(the department that item is in) and txdate (the date the product was sold).

As you can see below in the code my first SQL statement calculates the nettsales and the nettcost between a certain date ('2017-01-01' and the current date) and groups it into departments and uses the department table to provide the description of the department next to it. Then the second SQL statement caclulates the total stock value with (onhand*avrgcost) and groups it into a departments which also uses the department table to add the description of it in a column.

Now my question is how do I join these two SQL statements in a way that gives my all the columns in the first statement with the additional column containing the total stock value per department. So basically taking the second column of the second statement and adding it to the first statements columns.

Net Sales AND Net Cost Per department (first)

SELECT
    a.DEPARTMENT, 
    b.DESCRIPTIO, 
    ROUND(SUM(IF(a.TCODE = 'IN', a.AMOUNT, 0)) -
        SUM(IF(a.TCODE = 'CN', a.AMOUNT, 0)), 2) As NettSales, 
    ROUND(Sum(If(a.TCODE = 'IN', a.COST, 0)) - Sum(If(a.TCODE = 'CN', a.COST, 0)) As NettCost
FROM
    stoctran a 
LEFT JOIN
    department b ON a.DEPARTMENT = b.DEPARTMENT
WHERE
    a.TXDATE BETWEEN ;2017-01-01' And current_date
GROUP BY 
    a.DEPARTMENT

Stock Holding Per Departmnet (second)

SELECT
    a.DEPARTMENT, 
    SUM(a.AVRGCOST * a.ONHAND) As StockValue
FROM
    stock a 
LEFT JOIN
    department b On a.DEPARTMENT = b.DEPARTMENT
GROUP BY 
    a.DEPARTMENT

Answer 1

select net.*, stock.StockValue
  from (SELECT a.DEPARTMENT, 
               b.DESCRIPTIO, 
               ROUND(SUM(IF(a.TCODE = 'IN', a.AMOUNT, 0)) -
               SUM(IF(a.TCODE = 'CN', a.AMOUNT, 0)), 2) As NettSales, 
               ROUND(Sum(If(a.TCODE = 'IN', a.COST, 0)) - Sum(If(a.TCODE = 'CN', a.COST, 0)) As NettCost
          FROM stoctran a 
          LEFT JOIN department b ON a.DEPARTMENT = b.DEPARTMENT
         WHERE a.TXDATE BETWEEN '2017-01-01' And current_date
         GROUP BY a.DEPARTMENT) net
  join (SELECT a.DEPARTMENT, 
               SUM(a.AVRGCOST * a.ONHAND) As StockValue
          FROM stock a 
          LEFT JOIN department b On a.DEPARTMENT = b.DEPARTMENT
         GROUP BY a.DEPARTMENT) stock
    on (stock.department=net.department)