SELECT and JOIN when there is no value in the table?

Question

MySQL

Hello. How to select data from two tables with a join, but from the first table all the data, and from the second by id from the first: if such a record is found, then it, and if not, then 0. It seems that you can use IF or IFNULL, but something not so it turns out
UPD: Table example on sqlfiddle: sqlfiddle.com/#!9/f30a13/10

select descr, above, if(count(discount) > 0, discount, 0) from time_discounts left join categories on time_discounts.cat_idx = categories.cat_idx  where categories.tar_id = 87 and time_discounts.tar_id = 87;

So finds only one record, but not all. Those. should be displayed like this:
| descr | above | discount |
| Test 1 | 2.33 | 1.23 |
| Test 2 | 42.11 | 20.45 |
| Test 3 | 19.32 | 0 | <= there is no such cat_idx with such tar_id in the time_discounts table, but in categories there is
| Test 4 | 10.50 | 5.86 |

Answer 1

LEFT JOIN selects all records from the left table and their corresponding ones from the right table. So either use RIGHT JOIN or change the join order of the tables.

Answer 2

select IFNULL(discount, 0) from ...