Solve It with SQL: Removing Points from a Linked List

In this guest video, Natalka shows how you can use SQL to traverse a linked list of co-ordinates. She then demonstrates how to remove points that are not on a corner.

She does this using the analytic functions lag and lead.

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The Magic of SQL with Chris Saxon

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[yagexing]

This is awesome! we could probably also use the fact that corner point's two adjacent points have no common x or y value, something like:

with...-- omits testing data
select node from(
select '('||x||', '||y||')' node, ll.*, lag(x) over (order by sq) pre_x, lead(x) over (order by sq) as next_x,
lag(y) over (order by sq) pre_y, lead(y) over (order by sq) next_y from ll
) where (next_x != pre_x and next_y != pre_y)
or pre_x is null or next_x is null -- to include head and tail

[mongolwarrior]

Isn't that wrong? sequence went 10 twice in video 11:13.