Question

I want to use a JOIN to return a boolean result. Here’s an example of the data…

t1

id | data 
-----------
1  | abcd     
2  | 2425     
3  | xyz  

---

t2

id | data | t1_id |
-------------------------
1  | 75   |     2     |    
2  | 79   |     2     |    
3  | 45   |     3     |

---

So with these two tables I want to select all the data from t1, and also whether a given variable appears in t2.data for each id.

So say the variable is 79, the results should be

id |  data  |  t2_boolean
--------------------------
1  |  abcd  |  0    
2  |  abcd  |  1    
3  |  xyz   |  0

---

So I’m thinking some sort of join is needed, but without a WHERE clause.
I’ve been banging my head about this one. Is it possible? I really need it inside the same statement as I want to sort results by the boolean field.

As the boolean needs to be a field, can I put a join inside of a field?

Thanks…

Answer 1

You might have to do a bit of work to knock this into a format suitable for MySQL but does this help?

SELECT t1.id, t1.data, t2.id IS NOT NULL AS t2_boolean
FROM t1
LEFT OUTER JOIN t2 on t1.id = t2.id AND t2.data = 79