subquery - Correlated vs Non-correlated subqueries in SQL -
i working correlated , non-correlated subquery in sql , trying same results both types of queries. issue non-correlated subquery. query runs not return results. correlated subquery return results, should. need trying figure out if simple non-correlated subquery written incorrectly. appreciated. queries follows:
--non-correlated subquery
select * hr.bc_products p p.sku not in (select ol.sku hr.bc_orderlines ol); --correlated subquery
select * hr.bc_products p not exists (select ol.sku hr.bc_orderlines ol ol.sku = p.sku);
i figured out issue was. after looking through results of each query realized nulls affecting outcome. updated non-correlated subquery excluding nulls. updated non-correlated subquery works , looks this:
--non-correlated subquery
select * hr.bc_products p p.sku not in (select ol.sku hr.bc_orderlines ol ol.sku not null); hopefully avoid problem in future.
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