FULL OUTER JOIN with SQLite

Yes, see the example on Wikipedia.

SELECT employee.*, department.*
FROM   employee 
       LEFT JOIN department 
          ON employee.DepartmentID = department.DepartmentID
UNION ALL
SELECT employee.*, department.*
FROM   department
       LEFT JOIN employee
          ON employee.DepartmentID = department.DepartmentID
WHERE  employee.DepartmentID IS NULL

FULL OUTER JOIN is natively supported starting from SQLite 3.39.0:

2.1. Determination of input data (FROM clause processing)

A "FULL JOIN" or "FULL OUTER JOIN" is a combination of a "LEFT JOIN" and a "RIGHT JOIN". Extra rows of output are added for each row in left dataset that matches no rows in the right, and for each row in the right dataset that matches no rows in the left. Unmatched columns are filled in with NULL.

Demo:

CREATE TABLE t1 AS
SELECT 1 AS id, 'A' AS col UNION
SELECT 2 AS id, 'B' AS col;

CREATE TABLE t2 AS
SELECT 1 AS id, 999 AS val UNION
SELECT 3 AS id, 100 AS val;

Query:

SELECT *
FROM t1
FULL JOIN t2
  ON t1.id = t2.id;

db<>fiddle demo

I will belatedly pitch in my 2 cents. Consider the 2 simple tables people1 and people2 below:

   id   name age
0   1    teo  59
1   2   niko  57
2   3  maria  54 


    id   name weight
0   1    teo    186
1   2  maria    125
2   3    evi    108

First, we create a temporaty view, v_all, where we join with UNION the two opposite LEFT JOINS as below:

CREATE TEMP VIEW v_all AS
              SELECT p1.name AS name1, p1.age,
                    p2.name AS name2, p2.weight
              FROM people1 p1
              LEFT JOIN people2 AS p2 
              USING (name)
              UNION
              SELECT p1.name AS name1, p1.age,
                  p2.name AS name2, p2.weight
              FROM people2 AS p2
              LEFT JOIN people1 AS p1
              USING (name);

However, we end up with 2 name columns,name1 and name2, which may have a null value or equal values. What we want is to combine name1 and name2 in a single column name. We can do that with a CASE query as below:

SELECT age,weight,
                CASE
                  WHEN name1 IS NULL
                    THEN name2
                  WHEN name2 IS NULL
                    THEN name1
                  WHEN name1=name2
                    THEN name1
                END name
              FROM v_all

And we finally end up with:

      name weight   age
0    evi    108  None
1  maria    125    54
2   niko   None    57
3    teo    186    59

Of course you could combine the two in a single query, without having to create a temp view. I avoided doing so, in order to highlight the insufficiency of just 2 left joins and a union, which is what i have seen so far recommended.

For people, searching for an answer to emulate a Distinct Full Outer Join: Due to the fact, that SQLite does neither support a Full Outer Join, nor a Right Join, i had to emulate a distinct full outer join / an inverted inner join (however you might call it). The following Venn diagram shows the expected output:

To receive this expected output, i combined two Left Join clauses (the example refers to two identical built tables with partially differing data. I wanted to output only the data which does either appear in table A OR in table B).

SELECT A.flightNumber, A.offblockTime, A.airspaceCount, A.departure, A.arrival FROM D2flights A
    LEFT JOIN D1flights B
        ON A.flightNumber = B.flightNumber
        WHERE B.flightNumber IS NULL
UNION 
SELECT A.flightNumber, A.offblockTime, A.airspaceCount,  A.departure, A.arrival FROM D1flights A
    LEFT JOIN D2flights B
        ON A.flightNumber = B.flightNumber
        WHERE B.flightNumber IS NULL

The SQLite statement above returns the expected result in one query. It appears, that the UNION clause does also order the output via the flightNumber column.

The code has been tested with SQLite version 3.32.2