[Cloud] Question about NOT EXISTS

Hi all,

The execution plan for this query [1] indicates that it will be entirely based on existing indexes. Yet in practice, the query takes a long time to run. Why is that?

Also, interestingly, the execution plan for this modified version [2] is identical, but it runs almost instantaneously.

Lastly, I expect that last query to return no results (because the NOT EXISTS condition should not be met) but it does return a row. Why is that?

Thanks!

Huji

[1] https://tools.wmflabs.org/sql-optimizer?use=enwiki_p&sql=use+fawiki_p%3B...

[2] https://tools.wmflabs.org/sql-optimizer?use=fawiki_p&sql=select%0D%0A++p...