FULL OUTER JOIN with union subqueries

Question

I am trying to create an output with a similar behaviour to FULL OUTER JOIN, with UNION in mysql

The queires I am trying to combine are the same with different time frame parameteres

EXAMPLE:

Select * from (
SELECT GGPORTAL as portal, sum(oa.GGAMOUNT) as amount FROM orders as o 
        left orderarticles as oa on o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
        where o.GGDATE >= '2020-01-01' and o.GGDATE <= '2020-12-31' 
        group by GGPORTAL
        ) as t1
        LEFT JOIN t2 ON t1.GGPORTAL = t2.GGPORTAL
UNION 
Select * from (
SELECT GGPORTAL as portal, sum(oa.GGAMOUNT) as amount2 FROM orders as o 
        left join orderarticles as oa on o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
        where o.GGDATE >= '2019-01-01' and o.GGDATE <= '2019-12-31' 
        group by GGPORTAL
        ) as t2
        RIGHT JOIN t1 ON t1.GGPORTAL = t2.GGPORTAL
        WHERE t1.GGPORTAL IS NULL

ERROR:

Table 'server.t2' doesn't exist

Single subqueries:

| Portal | Amount    |
|--------|-----------|
|    3   |       250 |
|    4   |       300 |
|    8   |       400 |
|    9   |       500 |
|   10   |       600 |

| Portal | Amount    |
|--------|-----------|
|    1   |       250 |
|    3   |       200 |
|    4   |       350 |
|    8   |       450 |
|    9   |       550 |

Desired Outcome:

| Portal | Amount    | Amount2   |
|--------|-----------|-----------|
|    1   |       NULL|       250 |
|    3   |       250 |       200 |
|    4   |       300 |       350 |
|    8   |       400 |       450 |
|    9   |       500 |       550 |
|   10   |       600 |       NULL|

Question: What is the right syntax? Would there be better alternatives in PHP backend to combine the outputs of these queries?

Answer 1

You must repeat the subqueries in each of the unioned queries:

SELECT * 
FROM (
  SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
  FROM orders o LEFT JOIN orderarticles as oa 
  ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
  WHERE o.GGDATE >= '2020-01-01' and o.GGDATE <= '2020-12-31' 
  GROUP BY GGPORTAL
) t1 LEFT JOIN (
  SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
  FROM orders o LEFT JOIN orderarticles as oa 
  ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
  WHERE o.GGDATE >= '2019-01-01' and o.GGDATE <= '2019-12-31' 
  GROUP BY GGPORTAL
) t2 ON t1.GGPORTAL = t2.GGPORTAL
UNION ALL
SELECT * 
FROM (
  SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
  FROM orders o LEFT JOIN orderarticles as oa 
  ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
  WHERE o.GGDATE >= '2020-01-01' and o.GGDATE <= '2020-12-31' 
  GROUP BY GGPORTAL
) t1 RIGHT JOIN (
  SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
  FROM orders o LEFT JOIN orderarticles as oa 
  ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
  WHERE o.GGDATE >= '2019-01-01' and o.GGDATE <= '2019-12-31' 
  GROUP BY GGPORTAL
) t2 ON t1.GGPORTAL = t2.GGPORTAL
WHERE t1.GGPORTAL IS NULL

If you are using MySql 8.0+, you can simplify the code with CTEs:

WITH 
  cte1 AS (
    SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
    FROM orders o LEFT JOIN orderarticles as oa 
    ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
    WHERE o.GGDATE >= '2020-01-01' and o.GGDATE <= '2020-12-31' 
    GROUP BY GGPORTAL
  ),
  cte2 AS (
    SELECT GGPORTAL portal, SUM(oa.GGAMOUNT) amount 
    FROM orders o LEFT JOIN orderarticles as oa 
    ON o.GGAUFTRAGSNR = oa.GGAUFTRAGSNR 
    WHERE o.GGDATE >= '2019-01-01' and o.GGDATE <= '2019-12-31' 
    GROUP BY GGPORTAL
  ) 
SELECT * 
FROM cte1 t1 LEFT JOIN cte2 t2 
ON t1.GGPORTAL = t2.GGPORTAL
UNION ALL
SELECT * 
FROM cte1 t1 RIGHT JOIN cte2 t2 
ON t1.GGPORTAL = t2.GGPORTAL
WHERE t1.GGPORTAL IS NULL

Answer 2

I just don't see the point for union all here. Both queries are the same, only the date filter changes. So, use conditional aggregation:

slect ggportal as portal, 
    sum(case when o.ggdate >= '2020-01-01' and o.ggdate < '2021-01-01' then oa.ggamount else 0 end) as amount_2020,
    sum(case when o.ggdate >= '2019-01-01' and o.ggdate < '2020-01-01' then oa.ggamount else 0 end) as amount_2020
from orders as o 
left orderarticles as oa on o.ggauftragsnr = oa.ggauftragsnr 
where o.ggdate >= '2019-01-01' and o.ggdate < '2021-01-01' 
group by ggportal