fix - Where example for conflict+merge

[jsk95]

Problem

The current documentation for where after onConflict + merge does not seem correct.
Following the example, we receive the error column reference "x" is ambiguous.

Root cause

This is because in the where condition of a onConflict + merge, we have access to both the table and excluded.
https://www.postgresql.org/docs/current/sql-insert.html
https://dba.stackexchange.com/a/224167

So the alias of the column name is ambiguous between the table and excluded.

We can actually see the table name being directly referenced in the test case that this scenario was created for https://github.com/knex/knex/pull/4148/files#diff-57a163701cfad49b7c6cbdfb102667277345ba8de7e575f6966269b0c0d8d3a0R1557

Solution

We could update with a custom where condition to actually use table name
https://github.com/knex/knex/blame/4ca3dd5bc28e0665c5bed55026fac2ec45489d81/lib/dialects/postgres/query/pg-querycompiler.js#L37

but implicitly choosing one or the other feels dangerous.

So this proposal is just to fix the documentation that shows the feature to work.

[rluvaton]

The website repo has been moved inside the https://github.com/knex/knex repo. Please open a PR there instead: (the website will be under the docs folder)

[jsk95]

Thanks @rluvaton , closing this PR and have raised it here knex/knex#6020