Right Join does not return all the records from right side table

Question

I have two tables

Table 1 : assetdetail : itm_id,itm_slno,itm_desc,..

Table 2 : itmtype : typ_id,typname,..

Table2 Contains 6 different typname.

But when I use right join it returns only 4 records.

My query is :

SELECT a.itm_id,i.typname,a.itm_slno,a.itm_desc,a.itm_class from assetdetail
a right join itmtype i on i.typ_id=a.typ_id where a.itm_id!='234'
and itm_class='XYZ' group by i.typname

I need to get all the 6 typename records in the join query.What is the wrong with my query ?

Answer 1

In a right join , conditions on the first table need to go into the on clause, not the where clause:

SELECT a.itm_id, i.typname, a.itm_slno, a.itm_desc, a.itm_class
from assetdetail a right join
     itmtype i
     on i.typ_id = a.typ_id and a.itm_id <> '234' and a.itm_class = 'XYZ'
group by i.typname;

Non-matching rows in the first table have NULL values, which fail the comparisons in the where .

I would write this as a left join , however. Most people find the logic easier to follow: keep all rows in the first table, regardless of whether there is a match:

SELECT a.itm_id, i.typname, a.itm_slno, a.itm_desc, a.itm_class
from itmtype i left join
     assetdetail a 
     on i.typ_id = a.typ_id and a.itm_id <> '234' and a.itm_class = 'XYZ'
group by i.typname;

The conditions remain the same.