Question

I’m a little lot rusty with my SQL and this is driving me nuts. What in my head is a simple outer join for some reason isn’t working.

t1:
column1, column2
101, 1
101, 2
101, 3
102, 2

t2:
column1, column2
1, one
2, two
3, three
4, four

(Where t1.column2 -> t2.column1)

Given the tables above the dataset I’m looking for would be:
101, one
101, two
101, three
101, null

102, null
102, two
102, null
102, null

Maybe I’m over thinking it, I don’t know. I’m trying to get back 4 rows for any select, in this example where t1.column1=101 or t1.column1=102 etc.

Answer 1

SELECT
  td.column1,
  CASE WHEN t1.column2 IS NOT NULL THEN t2.column2 END AS column2
FROM (SELECT DISTINCT column1 FROM t1) AS td
CROSS JOIN t2
LEFT JOIN  t1 ON t1.column1 = td.column1 AND t1.column2 = t2.column1

A variation on the above (suggested by ypercube in the comments):

SELECT
  t1_d.column1,
  t2_2.column2
FROM (SELECT DISTINCT column1 FROM t1) AS t1_d
CROSS JOIN t2
LEFT JOIN  t1
  INNER JOIN t2 AS t2_2 ON t1.column2 = t2_2.column1
ON t1.column1 = t1_d.column1 AND t1.column2 = t2.column1