Question

I have two tables where I’m trying to select rows where a common field between those tables matches exactly, however it’s proving difficult to write the query. Here is a simplified version:

The tables look like this (simplified):

T1:
  id, name, sn

T2:
  id, location, sn

I’m trying to get t1.name and t2.loc together only where t1.sn=t2.sn. The sn field is unique in both, and so at the most, only 1 record will match between tables. In t1, all records have a sn field value, however in t2 about 30% of them have NULL for sn. So, I an expecting the join to produce somewhat fewer rows than t1 has.

How would I do the join?

Thanks.

Sample data:

t1:
+---+--------+-------+-----+
| id| name   | sn    | ... |
+---+--------+-------+-----+
| 1 | thing1 | 12345 |     |
| 2 | thing2 | 10000 |     |
| 3 | thing3 | 33445 |     |
| 4 | thing4 | 99223 |     |
+---+--------+-------+-----+

T2:
+----+--------+-------+-----+
| id | loc    | sn    | ... |
+----+--------+-------+-----+
| 90 | here   | 12345 |     |
| 92 | there  | NULL  |     |
| 96 | near   | 33445 |     |
| 99 | far    | 99223 |     |
+----+--------+-------+-----+

Result:
+--------+-------+-------+
| name   | loc   | sn    |
+--------+-------+-------+
| thing1 | here  | 12345 |
| thing3 | near  | 33445 |
| thing4 | far   | 99223 |
+--------+-------+-------+

Answer 1

SELECT
  t1.name AS name,
  t2.loc AS loc,
  t1.sn AS sn
FROM t1
INNER JOIN t2 ON t1.sn=t2.sn