left and right join

Question

Hi,

table 1

Table 2

select A.* from table1a LEFT join table2 b on a.col1=b.col1

output:

which is correct

but on right join

it shows above results how to calculate this join and how it will react on NULL and blank

Answer 1

If the left join gives you the correct result, use a left join.

A RIGHT JOIN B is the same B LEFT JOIN A. Personally, I never use RIGHT JOIN. It gives me a headache every time I see it.

Also, keep in mind that when joining two tables, no matter the join type, the join column(s) should be a unique key in at least in one of the tables. If they are non-unique in both tables, you will get a row explosion. That is, if there are three rows in one table and four in the other, all with the same key value, the join will produce twelve rows.