Re: Possible documentation inaccuracy in optimizer README

On Tue, 8 Apr 2025 at 16:28, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> We could possibly avoid the inaccuracy by making the examples use
> some other operators that are not equijoins. But I wonder if that
> would not be more confusing rather than less so.

I don't think it'd hurt to mention that we're just ignoring the
existence of ECs for this example. Something like:

--- a/src/backend/optimizer/README
+++ b/src/backend/optimizer/README
@@ -143,7 +143,10 @@ For example:
{1 2},{2 3},{3 4}
{1 2 3},{2 3 4}
{1 2 3 4}
- (other possibilities will be excluded for lack of join clauses)
+ (other possibilities will be excluded for lack of join clauses
+ (technically, EquivalenceClasses do allow us to determine derived join
+ clauses for this case, but we ignore that for the simplicity of this
+ example))

SELECT *
FROM tab1, tab2, tab3, tab4

If it'll stop a future question or someone from being confused, it
seems worthwhile.

David