Join tables where inluding null values on THIRD table

Question

I am working on e-dictionary and i have 2 tables:

First table: Term

+----+--------------+
| id | term_text    |
+----+--------------+
| 1  | hello        |
| 2  | how are you? |
| 3  | hola         |
+----+--------------+

Second table: Dictionary

<pre>
+-----------+------------+
| term_id_1 | term_id_2  |
+-----------+------------+
| 1         | 3          | /* hello - hola
| 2         | NULL       | /* how are you? - NULL
+-----------+------------+
</pre>

I want to display like this:

<pre>


+--------------+-------------+
| term_text_1  | term_text_2 |
+--------------+-------------+
| hello        | hola        | 
| how are you? | NULL        | 
+--------------+-------------+

</pre>

I was trying to get data using following query:

<pre>
SELECT t1.term_text_1, t2.term_text_2
FROM dictionary d, term t1, term t2
WHERE d.term_id_1 = t1.id
AND d.term_id_2 = t2.id
</pre>

But i was getting only where value is not null!

Answer 1

You need to join dictionary with term twice:

select 
  t1.term_text term_text_1,
  t2.term_text term_text_2
from dictionary 
left join term t1 on t1.id = term_id_1 
left join term t2 on t2.id = term_id_2 

See the demo.
Results:

| term_text_1  | term_text_2 |
| ------------ | ----------- |
| hello        | hola        |
| how are you? |             |

Answer 2

You can use LEFT JOIN

SELECT t1.term_text as term_text_1, t2.term_text as term_text_2
FROM dictionary d
LEFT JOIN term t1 ON d.term_id_1 = t1.id
LEFT JOIN term t2 ON d.term_id_2 = t2.id

Demo