How to multiply total of one column with row entry in SQL ie sum(column_name) * column name

Question

Unable to understnad how to use the formula of multiplying total of colum with entry of row.

Tried the code below

SELECT g.Item_No, (sum(g.units)* u.Unit_Percentage) as Units@2018Mix
FROM Global_GM_2019 g
FULL JOIN UnitMix_perc_2018 u 
ON u.item_no=g.item_no
GROUP BY g.item_no;

I get this eror which I know that should include all the columns in group by function.

Msg 8120, Level 16, State 1, Line 275
Column 'UnitMix_perc_2018.Unit_Percentage' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

Expected

Products    units of 2019   % of units of 2018  product mix
a              110                     34            20570
b              120                     23            13915
c              120                     12            7260
d              130                     12            7260
e              125                     23            13915

Expected result image added here

Answer 1

Try computing a summary table and then joining (this will probably run fastest as the join will likely be smaller).

Select item_No, unit_sum * Unit_Percentage as Units@2018Mix
From (
  SELECT item_no, sum(g.units) as unit_sum
  FROM Global_GM_2019
  Group by item_no
) as g
  FULL JOIN UnitMix_perc_2018 u 
  ON u.item_no=g.item_no

Or simply move the calculation into the sum

SELECT g.Item_No, sum(g.units* u.Unit_Percentage) as Units@2018Mix
FROM Global_GM_2019 g
FULL JOIN UnitMix_perc_2018 u 
ON u.item_no=g.item_no
GROUP BY g.item_no;

Or add the unit percentage scalar to tour group by.

SELECT g.Item_No, (sum(g.units)* u.Unit_Percentage) as Units@2018Mix
FROM Global_GM_2019 g
FULL JOIN UnitMix_perc_2018 u 
ON u.item_no=g.item_no
GROUP BY g.item_no, u.unit_percentage:

In reply to the comment stream... @sag, you are sort of cheating - you are asking two questions in one. The two questions are:

1. I have a syntax error in my posted query. (Saying " I know that should include all the columns in group by function" does not cancel this point out. If you know that, you should do that in your orignal post. Refer to create a Minimal, Complete, Verifiable example .)
2. I'm not going to tell you how it is stored nor how to calculate it, but I want to get some data from two years in my 4 columns of output.

I have answered question 1 three ways. I can only guess for question 2 (because you provide no details in your question on this subject). Here is my guess.

SELECT g.Item_No,
     sum(g19.units),
     (sum(g18.units)* u.Unit_Percentage) as Units@2018Mix,
     /* Maybe */ (sum(g19.units) (double) / sum(g18.units) * 100.0 as g19_pcnt_increase_over_g18  /*???*/
     /* I have no idea how you intend to calculate "product mix" because you provide zero information on this topic. */
FROM Global_GM_2019 g JOIN Global_gm_2018 as G18 on
       g.item_id = g18.item_id
FULL JOIN UnitMix_perc_2018 u 
ON u.item_no=g.item_no
GROUP BY g.item_no, u.unit_percentage:

We can only provide answers to the question that you have asked for which you provide some supporting information . Again, please refer to how to create a Minimal, Complete, Verifiable example .

Answer 2

I doubt that you really want a FULL JOIN , because you will get rows that are NULL .

Based on your description, I think you want:

SELECT g.Item_No, SUM(g.units * u.Unit_Percentage) as Units_2018Mix
FROM Global_GM_2019 g LEFT JOIN
     UnitMix_perc_2018 u 
     ON u.item_no = g.item_no
GROUP BY g.item_no;

In other words, do the multiplication before doing the SUM() .