Question

I would like to do as follows:

Select * from
table1  a
inner join table2 b

on

a.id = b.id

if (some condition is met) //  Now it gets interesting!

begin

and a.name = b.name

end

Obviously, this doesn’t work.

How can this best be accomplished?

Thanks Stackers!

Answer 1

I would use something like this:

SELECT * FROM table1 a
JOIN table2 b ON (a.id = b.id)
WHERE NOT ( == your condition here == ) OR a.name = b.name

If you really want to put it in the join condition, you could do something like this:

SELECT * FROM table1 a
JOIN table2 b ON (a.id = b.id AND (NOT ( == your condition here == ) OR a.name = b.name))

but I think the first form is more clear.

EDIT: as @James Curtis noted in the comments:

it is important to note that the option to put the condition in the
WHERE clause is only valid for an INNER JOIN, for an outer join you
may eliminate rows.