How to return null if not exists

Question

I'm using oracle plsql and I have a question. I have table of Tests and Table of Schools.

How can I make a query that will put null or some other by my demands?

I mean, to put null or some numeric number in the execution.

Have you tried something yet? A simple `LEFT JOIN` would probably do what you want. — Tim Biegeleisen, Dec 17 '16 at 11:25
I have no example. Just the idea. Have you any examply for this left join or something? — PythIsReal, Dec 17 '16 at 12:06
A "left join" is really a "left OUTER join", the important distinction here being between an INNER JOIN and an OUTER JOIN. Best of luck. — Bob Jarvis - Слава Україні, Dec 17 '16 at 13:13

score 0 · Answer 1 · answered Dec 17 '16 at 12:40

Maybe something like this:

Schools-table

create table schools (name varchar(20));

insert into schools values ('Harvard');
insert into schools values ('Oxford');
insert into schools values ('Cambridge');

Tests-table

create table tests (name varchar(20), school varchar(20));

insert into tests values ('Math', 'Harvard');
insert into tests values ('Math', 'Oxford');

Left join

select
    s.name,
    t.name
from
    schools s
left join
    tests t on t.school = s.name;

Output

|      name |   name |
|-----------|--------|
|   Harvard |   Math |
|    Oxford |   Math |
| Cambridge | (null) |

How to return null if not exists

1 Answers1